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Although Sarah was born in the UK, she and Felix were raised in North America by their Irish foster mother Mrs. S. Upon retrieving Kira she leaves her daughter with her ex, Cal, refusing to tell him about the clone conspiracy. Sarah battles Dyad and Rachel and soon discovers Helena survived much to her shock. When she digs into the origins of the experiment she is stunned to learn Mrs. S helped Ethan Duncan many years ago and remains distrustful of her foster mother. Sarah reluctantly considers bringing Kira to Dyad in order to try and save Cosima's life. Sarah arranges for Kira's bone marrow to be extracted and taken to Dyad for Cosima's treatment, however Rachel manages to kidnap Kira. Sarah surrenders to Dyad in hopes they will release Kira, Dyad plans on extracting one of her ovaries. Sarah's allies and Marion Bowles are able to arrange for Sarah and Kira to escape. Marion introduces Sarah to one of the male clones created by the military. Sarah is outraged at Mrs. S. giving Helena to the military and agrees to help Delphine trick Ferdinand into thinking Rachel is unharmed in exchange for help in saving Helena. After she, Kira and Cal are attacked by Rudy and Seth, Sarah has Cal take Kira to safety in Iceland and sets her sights on finding Mark.

Working with Art to track the Proleathans Sarah learns of Helena and Gracie's pregnancies and reveals Mark's clone heritage to Gracie. She finds Mark and informs him that they are siblings and watches as he is shot by Gracie's mother Bonnie. Sarah saves Mark and removes a bullet from his leg, while things are tense between them she learns the Castor clones were raised not to make any personal connections outside their brothers. They work together to find the remains of the original Castor DNA in Abel Johnassen's body. Sarah is then captured by Mark and Rudy. Upon waking up at the military base she is rebuffed by Helena who believes Sarah is why she has been put there. Sarah is furious at Paul for working with the military now and the deal he made with Mrs. S to sell out Helena. Paul claims the military is a family and everything he has done has been to protect them just as Sarah does for her sisters. Paul is unhappy she is a captive but is assured by Dr. Coady she will be unharmed, however she takes a gallon of Sarah's blood as a possible alternative to cure the Castor brothers. After telling of how she left Kira again to find Helena, the two sisters work together to escape. But once Helena is free she leaves Sarah behind, claiming they are now even. Sarah is injected with Rudy's blood and while fighting off the Castor sickness hallucinates and is told by Beth to stop focusing on why the clones were made but for who. Paul learns Dr. Coady is testing and researching the Castor defect that leaves their sexual partners sterile. It is the same defect the Leda's suffer from, attacking men's brains and women's fertile tissue. Once Paul realizes the higher ranks of the military are supporting Dr. Coady's efforts to weaponize the defect, he frees Sarah who fought off the illness. Killing Miller, Paul leads Sarah to freedom, telling her he regrets Beth's death and became her boyfriend to infiltrate Dyad trying to find a cure for the Castors. But he only ever loved Sarah. Going to Dr. Coady's lab, Coady refuses to focus on only finding a cure and shoots Paul several times. Paul detonates a grenade before he dies, destroying Coady's research. The blast knocks down Sarah in the nearby tunnels who is met and rescued by Helena.

At a Mexican bar the sisters are reunited with Mrs. S. Despite her concern Sarah lets them work out their issues alone. Sarah and Mrs. S later reunite as family informing each other of recent events and Sarah admitting she is very tired to her "Mom." Returning home Sarah reluctantly decides to have Rachel decode the book for a cure despite the other ways it could be misused and Mrs. S's concern that breaking the alliance with Delphine will leave them vulnerable to Topside. After unhappily stealing Krystal's information with Felix, Sarah watches as Rachel decodes one page of information before pulling her own con to escape. Believing Rachel to be in a coma, Sarah, Felix and Mrs. S decide to return to London to search for the Castor original.

Once there Siobhan's old contacts are friendly and a man named Terrance says he is close to finding the original so Siobhan can kill him. However, Terrance is tortured by Ferdinand and his bodyguard Bulldog, before dying of his wounds he tells Siobhan something. After Siobhan refuses to tell Sarah and Felix anything, they track the original themselves, leading them to Kendall Malone. Siobhan reveals this is her mother. Kendall explains her history with Ethan Duncan making them realize Kendall is the original donor for both sets of clones. Siobhan still considers killing her while Sarah pleads for her not too. They take Kendall back home, to a safe house provided by Art, so Scott and Cosima can examine her. Sarah and Delphine make a deal with Ferdinand to kill the Castors and neutralize Dr. Coady in exchange for genetic material from Kendall so Topside can make more clones. Her plan works, resulting in the death of Rudy and Dr. Coady's capture. She prepares to have some samples given to Ferdiand but is warned by Delphine the Neolutionists have manipulated everyone to get to this point including Ferdinand. Realizing Bulldog is a Neolutionist, Ferdinand kills him with a baseball bat and agrees to work with Sarah long-term. Sarah happily attends the dinner party with her family and friends. She, Siobhan and Kendall then reunite with Kira in the Icelandic snow.

At the start of Season 4, Sarah is woken up in the middle of the night to be warned by MK and Art that the Neolutionists are coming. Burning down their hideout and returning to the other clones, Sarah is hurt that Kira seems distant over missing Cal. Sarah and Art find old footage of Beth in her apartment and Sarah tries to find MK and an old Neolution lead. Sarah reconnects with Felix who has been ignoring her and ropes him into going to Club Neolution with her, though he is annoyed at how she uses him and wants to focus on finding his own birth family. Sarah poses as MK and is shown a video of the "Maggot-Bot" implant of Neolution that kills its hosts if tampered with. Stealing Dizzy's phone she talks with MK and learns a bit more of why Beth killed herself. She is attacked by the paramedic couple who think she is MK, they back off when they realize she is Sarah; but also reveal to Sarah she has a Maggot-Bot inside her.

Scared and unsure of what it is doing to her, she tries to recruit Felix to help, but he has found his biological half-sister Adele. She is a disbarred lawyer whose father admitted to having an affair with a British dancer when he died. Felix's mother died when he was little and the two found each other. Not admitting to the danger she's in, Sarah and Felix coldly dismiss each other. Tracking down Dizzy, she and Art try and reverse track the man in the video. Sarah ends up in a dental clinic thinking they can remove the Maggot-Bot, and a hygienist mistakes her for Beth. The hygienist says she can remove it but is actually a Neolutionist who deflected Beth before, and says the test subjects are lucky to have the Maggot-Bots. Sarah is saved by Ferdinand who kills the hygienist and tells her Susan Duncan is alive. Reconnecting with Siobhan and Felix, they work with Ferdinand who wants to protect Rachel. Sarah tries to get MK to reverse track Rachel's online message but MK disconnects when she hears about Ferdinand. Telling Dizzy they are clones, the two break into MK's trailer and learn MK is Veera from Helsinki. Realizing she has lured Ferdinand to Beth's, she is barely able to convince Veera not to kill him, but Veera refuses to help the still living clones and departs with Ferdinand's money.

Spending time with Kira, she tries to ignore the other clones but snaps at Alison on Art's behalf over the Hendrixes drug dealing. Still not trusting Adele, especially since the website that connected her with Felix is connected to Neolution, she has Scott run a DNA test on Adele and Felix. Felix loses patience with Sarah, bringing Adele to the safe house for dinner out of spite. Sarah's questions about how she found Felix annoy Adele, though Sarah is humiliated when Scott calls to confirm she is Felix's biological sister. Kira makes Sarah realize she is having more than dreams; Kira can somehow sense the mood of the Leda clones, even the ones she hasn't met. Sarah makes a deal with Susan to hand over Kendall's DNA and Cosima's data for a cure and to get the Maggot-Bot out of her face but will not give them the Castor genome as it contains the sterilization weapon. The deal is made behind Siobhan's back but she reluctantly goes along after Kendall agrees.

Evie and Susan reveal the Maggot-Bots have a different purpose for each host. Leekie's was to prevent Alzheimer's while Sarah's was to kill her with the Leda defect by reversing her immunity and provide a possible cure. After Evie and Cosima remove it, Sarah returns only to find Kendall has been taken. Capturing Susan, destroying Kendall's Leda sample, and hunting Ira, Sarah pieces together Evie was behind it all, including Beth attacking Susan. A devastated Sarah and Siobhan get Cosima's call that Kendall is dead. Siobhan blames Sarah for her death, and Sarah agrees, going on a self-destructive binge at a bar where Peaches (musician) is playing, getting high and drunk with a random couple and Dizzy. Going back to his place, she wants to have sex with him but Dizzy questions how she got the Maggot-Bot out, he was friends with Ed, the first person with a Maggot-Bot that Veera and Beth has uncovered. Sarah doesn't want to talk about any of the clone business but is haunted by a vision of Beth. Sarah goes to a bridge above the train station and considers throwing herself on the tracks to die, just like Beth. Kira can sense Sarah wants to follow Beth which allows Felix to find her, saying Sarah can be stronger than Beth. The image of Beth tells Sarah to bring all the clones together before fading away. Siobhan is able to forgive Sarah.

While Kira plays a computer game, Veera appears and Kira recognizes her as the girl in the shadows. Warned by Veera that Evie will come for them, she and Cosima patch themselves through to Susan's northern island hideout. Kira warns Sarah that Siobhan has left with her rifle. Calling in Art to warn him Siobhan might kill another cop in Duko, they are relieved that Siobhan didn't snipe him but alarmed to hear Duko is meeting with Alison. Sending Felix to Alison's rehearsal for information, they are able to trap Duko at the comic shop. Duko pleads for Art's help but Art had already crossed the line for Beth. Under Siobhan's torture he reveals Evie sees Sarah as a threat and using the Maggot-Bots as a gene therapy is only a cover for something else. Duko claims he only works and was paid by the Neolutionists to protect and provide for his ten year old niece; he did bad things for his family. Siobhan agrees and shoots him dead as revenge for Kendall.

Sarah reluctantly has one of her eggs removed to be mixed with Ira's sperm as a possible cure for Cosima and the clone sickness. Very reluctantly she and Felix meet with Rachel and Ira to take down Evie, but rebuff their offers to help find the BrightBorn mothers.

Sarah goes with Art to a woman's shelter where one has apparently killed herself. Another cop there asks Art about Duko and is revealed to also be working for Evie. Sarah sees Trina who was friends with the BrightBorn mothers. Posing as Beth, Trina tells her Kendra and her baby Jacob are probably in Tisdale. Tracking them down, Kendra says her baby was born blind, so they probably will both be killed like the deformed newborns at BrightBorn; of which Kendra has video proof. Sarah refuses to blackmail Kendra into going with them like Rachel wants so Rachel calls Kendra and has Ira take her. Art and Sarah are interrupted by Roxie the paramedic and another man; likely the ones who killed the surrogate at the woman's shelter. Art arrests them. They later confront Ira for betraying them but are amazed when Rachel is able to discredit Evie and BrightBorn to the media. Sarah is thrilled when Cosima announces she found a cure but alarmed when communication is suddenly cut off. Krystal contacts Felix about Delphine, forcing him to reveal Sarah as a clone but Krystal denies they look alike. Posing and Krystal she and Siobhan capture Dr. Van Leir who says his orders to save Delphine weren't from Evie; Neolution follows the best science to advance evolution and Rachel is setting up a grab for power. Convincing Ira to get her a helicopter, she goes to the island alone, convincing Siobhan to stay with Kira. Kira can sense many clones they haven't even met yet, and Sarah promises to find a cure for all of them. She finds a bleeding Susan sewing herself up with Rachel having taken the gene line. Rachel sneaks up and brutally beats her with her cane, saying Sarah is nothing but a cockroach that didn't know anything until she saw Beth; while Rachel was raised for this. Though Susan tries to help Sarah, Rachel stabs Sarah in the leg. Susan's distraction allows Sarah to limp away. Dragging herself to the beach she calls Siobhan for help, only to hear Ferdinand has captured Siobhan and Kira.

Sarah stumbles through the island, scraping together a fire and makeshift bandage for her leg. A rabid human-like creature attacks her and rolls through the fire before fleeing. She has visions of Kira urging her to awaken whenever she sleeps. Using the last of her phone power to call Felix, she follows Ira's instructions to the boathouse but men with tracking dogs are after her. Something in the wilderness hunted and took a massive bite from a wolf. Sneaking into Revival she meets Cosima in the medical trailer but Cosima chooses to stay on the island. Cosima aids Sarah in getting away. Sarah goes back to the boathouse only to be tranquilized by one of the men. Rachel stands over her, proclaiming it to be a new day. Taken back to mainland and awoken in Dyad she tries to reject Rachel's offer of only some visits to examine Kira but Siobhan and Kira tell her to take it. The house and Kira's route to school are under constant watch, so Felix sneaks out to make arrangements with MK. MK says she can get them out if they can sneak Kira out of school. Sarah pretends to be Rachel to get Kira out of class and loses the man tailing her. She goes to Felix's loft to try and convince MK they can help her but she is followed by Ferdinand. Sarah reluctantly leaves MK but when she meets back with her family, Kira feels MK die. Kira refuses to flee wanting to know why she has abilities and demands Sarah take her back. Sarah, Siobhan and Felix are forced to watch as Rachel takes Kira. That night Siobhan is visited by Delphine who doesn't want anyone else to know she is communicating with Siobhan. After holding a memorial for MK, Sarah is hurt and alarmed Kira won't tell her what she does when she meets Rachel. She hangs out in Felix's loft to try and cool off but rushes to the Hendrix home when Donnie says the cops are all over it. She refuses to let Donnie give up Helena's location and is relieved when Alison deals with Rachel. Unbeknownst to anyone, Kira is implied to be cutting herself to test her healing factor. Kira is most irritated by Sarah's questions, admitting Rachel took blood and fingernails from her and that she cut herself to see how fast she could heal; it doesn't hurt her. Siobhan has Scott and Hell-Wizard researching Westmorland's history, the last known record of him was disappearing into the jungle in Borneo in 1894. Siobhan says they only have 3 days until Kira's next appointment at Dyad and they need leverage. She has Felix take Kira for the night and tells him to prepare for a visitor. Meanwhile, she and Sarah prepare a con to steal the ID of psychologist Elizabeth Perkins. She says this will get them into a mental hospital to see a patient who has information on Westmorland but Siobhan won't reveal her source for the information. While distracting Perkins, the psychologist says Siobhan's daughter is on the edge of becoming like Siobhan. With the fake ID Siobhan poses as Perkins with Sarah as her assistant, warning Sarah to keep calm. The patient is a heavily drugged Virginia Coady under a false name. Snapping her out of it Sarah briefly attacks her for what she did to Helena, Paul and the sterilized women. Coady says Susan Duncan put her in there. Westmorland and Susan recruited her when she was young and before the cloning started. They had found a boy with a unique genome and the crude science caused brain damage, tumors and physical deformities. Susan wanted to stop but Westmorland and Coady pushed forward until the subject got out of control. Westmorland separated Susan and Coady into the two separate clone projects afterwards. She wants out of the mental hospital to tell them more. When they are about to be caught by the staff, Coady creates a distraction by trying to strangle Sarah, letting Siobhan and Sarah slip away and Coady grabs Sarah's visitor pass which has a key card to unlock the doors. Meanwhile, Kira tells Felix her mother is acting dumb because of Rachel and Kira is actually trying to help her mother. Felix's visitor is Adele, whom Siobhan told about the clones. Adele says she was disbarred as a lawyer for embezzling money and she has word of six Neolution subsidiaries in Switzerland, wanting Felix to come and help her track them. He eventually agrees. At home with Kira, she offers to start telling Kira about the adult stuff if Kira opens up about the connection she has to the Leda clones. Siobhan has Scott and Hell Wizard tracking the origins of Neolution and how the cloning began trying to find out if the man on the island really is the 170 year old Westmorland. Giving code names for the clones, Kira says she wants to help and be a hustler like her mother, and the first step is gaining someone's trust by giving them what they want without them realizing what's happening. Delphine appears soon to meet with Felix in Geneva, giving Siobhan a flash drive on what she knows they intend for Kira. Delphine asks if Siobhan's source that found Coady can help them again; Siobhan is unsure and Delphine says Kira is running out of time. After faking Kira being sick to avoid her next Dyad appointment, she is brought in to deal with the Krystal and Brie. Wanting to question Len Snipp herself she prepares to pose as Krystal but Krystal takes the mission herself, forcing Sarah and Art to watch her make out with him and clumsily get information. When Scott tells them Len's prototype face cream is what caused Brie to lose her hair, Sarah is impressed as Krystal beats Len up. Rachel arrives for Kira that night and Siobhan warns her that she will need them one day. Kira tells Siobhan not to worry and that she'll finish her book, Kira code-names the island Wonderland. Kira is given several biopic tests at Dyad and makes Rachel a friendship bracelet to try and make Rachel care for her. Westmorland tells Kira over video he is counting down until they meet. Eventually, Kira is able to use her code to warn Sarah over video call, that Rachel is planning on sending her to the island. Sarah is horrified. Cosima gives her Westmorland's real identity, John Patrick Mathieson, born into an oil rich family in Texas during 1939. She has this information sent to Rachel and calls her, begging for Kira to be spared but Rachel acts unmoved. Art rushes in taking Sarah and Siobhan to Dyad as Rachel decided to sneak Kira away. They return home as Siobhan watches over them. After sending the kids away, Siobhan wants the sisters to focus on Felix's art gallery opening that night, featuring portraits of all the Leda clones. Sarah has the nagging suspicion she is hiding something with Delphine, still wondering about the source. Adele has some drinks and says Delphine and Siobhan are doing whatever it is for them but mentions meeting a guy named Ferdinand, disgusting Sarah. At the art gallery Colin the morgue attendant shows up to rekindle things with Felix, agreeing to stay silent on his multiple sisters. When a high ranking art dealer shows up Alison convinces Felix to pass off the clones as one individual dressed in his paintings as a performance art, securing a deal for Felix's career. At home Siobhan cries as she writes a letter. Throughout the night, Scott, Hell-Wizard, Adele, Art, Cosima, Delphine, Donnie, Alison, Siobhan and Sarah all filter in and out in support of Felix. When Sarah confronts Siobhan she says it was all to free the clones and that Rachel has given them hard evidence of Neolution's endgame: control evolution and extend the lives of the rich while sterilizing everyone else and having governments pass legislation to get a database of everyone's genetics. Rachel gave Siobhan the hard evidence of decades of death and illegal experiments to expose Neolution to the world. With the sisters believing they are free, Felix introduces Sarah as the "true form" of his sister and thanks her, and Adele for being in his life; along with Siobhan for bringing them to Canada and nurturing them. Rachel calls Siobhan to warn that Ferdinand survived the board and will be coming for her. He is at her home and while she convinces him they can both put their guns down, he shoots her with Siobhan's own spare gun. Siobhan asks that he give her a picture of Sarah and Felix to hold, he sneers and throws it on the floor; but while his head is turned, she grabs her third gun and shoots him in the neck, mocking him as he dies. Siobhan holds the picture of Sarah and Felix. While dancing at the gallery, Sarah feels Siobhan die. Sarah hosts the funeral with Kira, Felix, Adele, and allies of the clones, along with Siobhan's old friends; saying she died to protect her family. At the wake, the silent nun shows up letting Sarah know Helena was taken. Though Siobhan left a note not blaming Rachel, Sarah is still furious, staying with Kira while Art and Felix interrogate her. With the investigation into Dyad and Neolution gone public, the police station is swarmed by Interpol and Engers has started to implicate Art. Taking a chance that his superior is not with Neolution, Art is given files on two recent murders. Most of Westmorland's board is being killed off including Van Lier. Rachel tells them where to find Al-Khatib at the conference room. Felix and Art find him there, about to be killed by Mr. Frontenac. Frontenac reaches for his gun and Art kills him. Though knowing his career and possibly more are ruined they continue pressuring Al-Khatib; who doesn't know where Helena is but that they would want Rachel. With Kira sensing Helena's babies coming, Sarah poses as Rachel in the trunk of Al-Khatib's car and is then driven by Engers to Mathieson while her allies track the car and Art follows. They are in the abandoned asylum wing of Dyad, right next to the main investigation. Sarah-as-Rachel tries to stall Mathieson but slips and calls him Father which Rachel never did. She nicks him in the neck with a knife but is caught by Engers. Before she is killed, Coady says they need her blood to save Helena. Sarah begs Helena to wake up. Art's entering the old wing triggers an alarm that Engers investigates, leaving the sisters alone with Coady, whom Helena attacks. Sarah frees Helena but her water breaks before they can escape. Stumbling to the basement Sarah gives Helena a piece of pipe to defend herself with while she looks for medical supplies to help with the birth. Mathieson is becoming increasingly weak and unhinged, injecting adrenaline and killing one of the doctors for disagreeing. He prepares to fly away on a helicopter with the twins since the delivery room has been compromised. Art sneaks in and knocks out Engers. Sarah evades Coady and Art gives her a spare gun. Sarah returns to the delivery room while Mathieson skulks around her. He claims ownership of them even though the twins grew up outside the experiment, stating they only need one of the unexpected twin clones; the fertile freaks. He attacks, trying to smother with one of the lab curtains, she manages to shoot him in the chest. Sarah says she and her sisters survived him, this is evolution. Mathieson babbles on about how the clones were his greatest creation and mistake and they'll always think of him in their origins. Sarah bashes his head in with his own oxygen tank to silence him forever.

Flashbacks show Sarah considered an abortion but decided to keep her baby, Siobhan saying she needs to be still and stable to be a mother. Siobhan coached her through the birth. Sarah draws on this as she and Art help deliver Helena's twin boys. Three months later, Felix returns from a successful art show in New York as Sarah studies for her GED. She has placed Siobhan's house up for sale and walks away before the test. Though Alison and the others want her to stay she snaps that the house is where Kira's grandmother was murdered. After the baby shower she admits with nobody left to fight, she feels like the same horrible mother with no plan like she always was. Her sisters calm her by relating their own maternal struggles. She listens to Helena's memoir that begins with Sarah stepping off the train. She is shocked at how many Ledas there are. The series closes as Sarah and Felix take Kira to the beach, Siobhan's home and her extended family providing the stability Sarah needs to be happy.

The Season 4 premiere reveals much about Beth's life prior to her suicide. After being contacted by the clone MK and finding Alison and Cosima, MK tells her to investigate the murder of a low-level Neolutionist. Her journey alerts Oliver and she briefly meets Leekie and Evie Cho. MK has convinced her Paul is a spy fueling her paranoia of her boyfriend. High on pills and drunk she tries to throw herself at Paul with passion; he acts cold but will also not be the one to end their relationship. In her misery, Beth almost shoots him. She runs to Art and has sex with him. Later that night she gets a tip from Trina who is concerned about her boyfriend, who has undergone an experimental procedure and was subsequently abducted by Neolutionists. While investigating, she follows Trina's directions to an alleyway, where she sees a parked ambulance. Trina instructs her to climb the fire escape, and when she does, she looks into a room and she sees the Neolutionist paramedics, Frank and Roxie, and Detective Duko, a detective from her police precinct, removing a worm implant from Trina's boyfriend's cheek. Still high, she crashes into boxes on the fire escape, startling the Neolutionists inside the building who then motion to follow her. While fleeing, she accidentally shoots Maggie Chen on impulse, who she believed was associated with the Neolutionists that were after her. Although Maggie Chen's sinister motives were revealed after Beth's death, Beth believed she had shot an innocent bystander. After learning Duko would be her legal representative, she flees to MK's trailer emotionally broken. MK promises to do the thinking for both of them. Beth is visited in her home and threatened by Duko. On the night of her, suicide Beth wore a disguise with a blonde wig, taking a gun and a card somewhere. She returns home with someone else's blood on her hands and meets MK. Ditching her disguise, she refuses to say what happened, giving MK the gun and telling her everything is over and to go back into hiding. She gives MK a hug and leaves to kill herself on the train platform. In the present, while Sarah tracks the dental lead, Art confronts Duko about visiting Beth's home and he tries to play it off as regular business. Present day information reveals she had a falling out with Trina, who was some kind of "carrier" and the night Beth wore a disguise, she was carrying a card for the Life Spring fertility clinic. At a cocktail party there that night, Beth confronted Susan intending to kill her as the head of Neolution to free her sisters. Susan says she has dedicated her life to the clones and is sorry about what Beth's father did to her mother Ruth. Susan had watched Beth graduate the police academy. Susan explains without her all the Ledas will die of the sickness. Beth lets Susan go, but then attacks her source; Evie Cho, scarring her face and covering Beth's hands with her blood. Evie had set Beth up to kill Susan so Evie could become the Neolution leader. Evie warns with what Beth has just done, Neolution will kill everyone in her life including Alison and Cosima, the only way to save them being if Beth kills herself. After Duko confirms clones have been wiped out before, Beth returns home and then chooses to die at the train station as her last act of protecting her sisters. When Sarah is suicidal after Kendall's death she speaks with an image of Beth. When Felix talks her out of suicide, Beth tells Sarah to bring all the clones together.

Season 5 flashbacks reveal Alison didn't believe Beth saying they were clones, so Beth had Cosima suddenly show up outside Alison's house one night. Sarah and Art have a moment of remembrance in front of Felix's painting of Beth at the art gallery.

The canon "Classified Clone Reports," an in-universe novel revealed Beth was molested for several years by her adoptive father until she was a teenager. Her monitors at the time of a neighbor, school counselor and pediatrician never saw it so Dyad was unaware of the abuse. Though her parents divorced, Beth cut all ties with them both after high school.

She signed a contract offered individually to herself, Sarah, and Cosima with the Neolutionists that supposedly freed her from further monitoring without knowing that they had "patented" the clones when they were created. Alison soon discovers that Donnie is her real monitor, this coupled with her guilt over Aynsley's death led her to abuse alcohol and prescription pills. Eventually she is forced into rehab by Donnie and befriends Vic, not knowing Vic is monitoring her for the police. Felix and Sarah are able to discredit Vic. It is revealed Donnie had no idea about the clones and thought he was part of a long-term sociology study he started in college. Donnie is furious Dr. Leekie ruined his family and accidentally kills him. Alison and Donnie bond over the deaths they caused, burying Leekie under their garage floor and rekindling their romance. Donnie intimidates Vic and Angie into staying away from their family.

Donnie is fired from his job and Alison decides to run for school trustee after helping Sarah and Delphine fool Ferdinand. Alison buys the prescription pill supply from her drug dealer who leaves town, intending to sell them for income and use the customer list as her voter support in the school election. Alison begins making and selling her products as well as gaining political support, turning down a bribe from Marcie to move to a nicer house outside the school district. Alison is confronted by higher-up drug dealers only to discover their boss is her ex-boyfriend from high school, Jason. They reunite on friendly terms and she agrees to increase his profits from her sales. Alison and Donnie enjoy twerking in their underwear while throwing their drug money around. Donnie buys a new car, to Alison's annoyance. They continue their operation and Alison informs Jason she intends to buy her mother's beauty shop Bubbles to make a drug front. Alison's mother Connie is very manipulative, condescending and judgmental initially refusing to sell them the store as she doesn't want Donnie as a co-owner. The same day as the school debate, Donnie and Jason try to buy more pills from the same drug dealer that cut off Vic's finger, Pouchy. A mix-up of the money and campaign materials almost costs Donnie his nose. Fortunately, with Felix and Cosima covering for her Alison is able to get the money in time to save Donnie. Alison is able to give a rousing speech about family to the voters. Jason convinces Connie to sell the store as Alison would be the true boss. Jason then kisses Cosima, thinking she is Alison. Connie reveals she did everything to get the best child, even going so far as to secretly request a sperm donor at the clinic instead of her ex-husband's material in order to have a baby with better genes; and hopes Alison will find the same courage to leave Donnie, perhaps for Jason. Out of spite Alison introduces Cosima as her clone, but Connie doesn't believe her and thinks the clinic gave another family the same sperm, making Cosima her half-sister; to Alison's exasperation.

While making soap in the shop as a cover for the drugs Alison happily takes in Helena and Gracie. When confronting Jason about his feelings for her they kiss and she enjoys it but reiterates that she is married and this is just business. Jason warns they are all stuck with each other now. Donnie confronts Jason alone in the shop and Jason mocks him and beats Donnie in a fistfight. Alison spends the next day campaigning while drug dealers from Pouchy demand the pills back from Donnie since Jason is no longer backing them. Donnie returns the pills but they laugh at his request for his money back. Once they threaten the Hendrix children, Helena slaughters them and gets back more money than Donnie expected. Alison is surprised by Donnie's bruised face and the cash when she returns home. On the voting day, Donnie surprises Helena by finding Jesse for her to her delight. Rudy follows the Hendrixes from the school, fortunately they were expecting him and lead him to a trap where Helena kills him. That night they host a dinner party at Bubbles for Sarah, Felix, Siobhan, Art, Cosima, Scott, and Helena where Alison learns she won the election by 56 votes and gives a speech on how they can face whatever comes next together as a big family. Flashbacks reveal Alison funded Cosima moving from Berkeley to help the clones and that she gave Beth a clean urine sample to pass the police drug testing. Alison tries to be happy that Helena is having twins but is clearly jealous. She also encourages Felix to be honest about his search for his biological family.

Upon learning of the Neolution implants, she assumes Leekie must have one, and she and Donnie dig him up while being repulsed by the decomposing body. After Donnie and Helena deflect the detectives investigating the murder of the drug dealers, Alison and Donnie tell Cosima how Leekie died and that they now have a Maggot-Bot to study. Alison wants to prepare for another musical but it mistaken for Beth by Trina. Once Sarah snaps at her to pull her weight for the clones, Alison sends Felix and Donnie to the Life Spring clinic to pose as a gay couple looking to have children. After dirty talking Donnie through a sperm sample, she notices a friend who also had fertility problems is now pregnant. Fishing for information and her genuine desire for her own child, Alison is told about the BrightBorn program which ties to the Neolutionists. With Sarah ignoring the clones, Alison has Donnie go with Cosima to a BrightBorn orientation as Cosima has the best scientific understanding. Detective Duko tells Art they have connected the Hendrixes to dealing pills at Bubbles which could connect them to the murders. And that Art should focus on his biological family. Knowing he had dinner at a drug front and his career is on the line, Art warns Sarah who warns Alison. Alison argues that was necessary to keep their house and is over now. She tells Sarah that Helena left with camping gear but she is not responsible to watch Helena, going about her own domestic life.

Alison is hurt by Kendall's death but refuses to talk about it, insisting on throwing Gemma's sleepover birthday party like normal. Art finds and beats Duko for killing Kendall and leading Beth to Evie which led to her suicide. Duko says there is nothing Art can do about any of it as he is also being watched for aiding Sarah and the Hendrixes; also hinting he knows how Art covered up Beth's shooting of Maggie Chen. While telling the kids a ghost story, the police bust in and arrest Donnie for dealing narcotics. Duko arrives to say he will be keeping in touch with Alison. In jail Donnie is threatened and beaten up by another Neoultionist inmate. Felix brings them Adele to be his lawyer, telling her Alison is Sarah's twin. In the two days it will take to get bail, Duko tells Alison he will have Donnie killed unless she gives him Sarah's location. Alison struggles with the choice and talks to her priest who tells her to do what she needs to for her husband. When Felix comes to speak with her she lies about Duko threatening her and then tells Duko that Sarah will be at the comic shop that night. However, this is a set-up to trap Duko. Once he is captured he is forced to call off the hit on Donnie. Alison is able to happily complete her rehearsal of Jesus Christ Superstar. Donnie is bailed out and eager to have sex with Alison since the kids are away with Connie in Florida. Meeting with Adele and Felix they are surprised their house is under surveillance but Alison slips up by saying it cannot be Duko. This makes Adele suspicious. After sex, Alison talks about how she has lost her faith and community and wants to go somewhere else. Since Donnie gave up his passport, they settle for the nearby Niagara Falls. While packing, Frank the paramedic captures Donnie, then Alison in the basement. He ties them both up and demands Alison tell him what happened to Duko or he will kill her with a Maggot-Bot. Alison tells Donnie she loves him and starts her final prayer. At the last second Helena busts in and kills Frank with an arrow to the throat, saving the Hendrixes. Alison and Donnie hide into Helena's hut in the woods. Although Alison hates living there, she is grateful for her 'avenging angel' Helena.

In Season 5, despite Art and Felix wanting them to stay put, Alison packs the hut to return to help the others. Warned by Helena, Donnie is able to escape but men abduct Alison from the woods. Art's new partner Detective Maddie Engers, points out to him the Hendrixes drug dealing; but who the Neolutionists really want is the pregnant crazy one, Helena. Engers implies harm to Art's daughter if he doesn't comply. Taking Alison to the middle of a road, Engers says she cannot harm the clones but holds a gun to Art's head. Engers demands Helena's location. Alison doesn't know where she is and Engers believes her, telling Alison she will be taken home. In her craft room she is forced to stay home by Engers until Helena and Donnie resurface. Helena's attack on the doctor at the hospital lets Donnie slip away. Flashbacks reveal she rejected Beth saying they were clones and got high on magic mushrooms one night with Anysley and Chad. Beth had Cosima drop in but Alison sent her away. Seeing the different paths her sisters took while high gives Alison an existential crisis as she is just a housewife. Anysley is able to say they have a good life but if Alison feels like she has a bigger purpose, she should commit to it; inspiring Alison to support the other clones. In the present she feels guilty for being unable to help save MK and Mr. Frontenac calls her the least valuable of all the clones. Alison pops a pill and tries to go back to her community to help prepare for the neighborhood Fall Fair. She finds she has been replaced as organizer and most people no longer like her. She slips the other pills into a juice and almost gives them to her replacement but stops herself. She is devastated upon seeing Chad and Anysely's two children now without their mother. Spotting her ex-drug-dealer Ramon she gets drunk and high with him; lamenting she doesn't know who she is anymore and thinking privately the clones have ruined her life. Donnie prepares a Highland Dance routine but is met by Art and Engers who have a search warrant on the house for the murder of Pouchy and the drug dealers. An alarmed Donnie warns Alison and calls Sarah, telling them that both Leekie and Rudy are buried in the garage. Finding nothing in the house, Art finds Engers planting bloodied clothes from the Pouchy murder scene mixed with clone blood to be evidence to arrest Donnie, but Engers then sees the garage floor and starts digging. Alison almost tells Chad about her role in Anysley's death but Chad says the best way they can honor Anysely is to move on and live their lives. Donnie drinks the juice Alison drugged. He twice collapses on stage during his routine. When the people make fun of him, Alison admits to being an alcoholic and pill-popper but calls them a bunch of hypocrites because half of them bought pills from her, imagining Anysley supporting her from the audience. She proudly proclaims to be part of a sisterhood they could never understand while helping Donnie along with Felix. Once Alison realizes Engers will find the bodies in the garage, she brings Leekie's head and for the first time meets Rachel. The head was previously examined by Cosima and Scott. She says any legal trouble for her and Donnie will expose Dyad and Neolution. Rachel is forced to call Engers off, saving her as Art was prepared to shoot Engers in the back of the head otherwise. Rachel admits to wanting to strangle Alison and Alison says the feeling is mutual. Alison and Donnie celebrate but a much calmer Alison says she needs time away to visit the kids and find herself, singing Ain't No Mountain High Enough with Donnie for a moment of happiness.Upon her return she has a haircut with a purple streak and tattoo on her hip. She met some people on her journey that taught her to live well and embrace her impulses; as burying them leads to negative behavior like her drinking. Donnie is especially surprised she wants to turn the craft room into a music room and she doesn't want to tell him what to do in life anymore. The two help set up the paintings. Though Felix says he cannot have multiple Ledas at the opening, Alison convinces him to swap them out individually as performance art to impress the crowd while Donnie acts as bartender. She and Cosima discuss the funeral, Alison worried Sarah hasn't cried yet.

Three months after the fall of Neolution, Helena and the twin boys live in the Hendrix garage. Donnie has become regional manager of an architect company. Sarah, Felix, Kira, Adele, Colin, Cosima, Delphine, Scott, Hell-Wizard, Art, his daughter Maya, Charlotte and Gemma all happily attend a backyard barbecue; hosted by the Hendrixes as Helena's baby shower. Alison relates her own struggle of scaring Gemma as a parent, calming Sarah. Alison's final shot in the series is playing happily in her music room after Donnie comes in from a run. He does a striptease amusing her. Alison and Donnie affirm their love for each other.

After Delphine dumps her she begins working on the genome in secret with Scott. The two meet with Dr. Nealon of Dyad and are told the originals that Projects Leda and Castor were based from were chosen by the Duncans and the data on both has been long lost. They then dissect Seth's body in Felix's bathtub, removing the brain and discovering the sibling relationship between the cloning projects. Their research hits a roadblock without some DNA from the one of the originals. Spending time with Felix he gets her into online dating to get over Delphine. Meeting Shay, a holistic healer, the two bond quickly and Cosima briefly mentions her break-up with Delphine. While on the date someone takes pictures of them in the distance. Cosima is nervous, but decides to have sex with Shay in Felix's apartment. The two quickly develop an intimate relationship. Returning to Dyad to examine Gracie, she acts cold to Delphine who is upset that Cosima has been keeping secrets and misses her. Cosima considers slowing down with Shay and is informed by Scott that Rachel may know the code to the Leda genome. Delphine is revealed to be the one behind the pictures and video of Cosima and Shay, watching them obsessively while drinking. Delphine interrupts them one morning demanding a urine sample from Cosima for further testing while Shay secretly listens.

Not trusting Delphine's new position at Dyad, Cosima seeks urine from Alison. She begins coughing again while posing as Alison for the campaign and fumbles the opening of Alison's debate speech. Alison refuses to give her any urine and chastises Cosima for shutting out Dyad when she needs them for her health. Cosima admits to Shay she has a serious disease and begins heavily bleeding from her crotch. She returns to Dyad, bringing Shay as a visitor who glimpses Ethan's coded book. Still not trusting Delphine, she works to free Rachel with Scott and Sarah in order to decode the book, but not tell Topside so they can't make more clones. After Rudy gets the book they lie to Delphine again by saying they made no copies of it. While Scott sends Rachel to Sarah, Cosima distracts Delphine by telling her she is resigning from Dyad and of her near-death experience. Delphine briefly softens kissing her again but warning her anyone outside Dyad could be a mole-perhaps Shay.

Dr. Nealon gets the copy of the book but it is useless with Rachel apparently comatose. Delphine accepts Cosima's resignation and fires Scott for all the lies they told but gives them a file on Shay. The file reveals Shay is involved with the military making Cosima think she is the mole, so Cosima goes back to Delphine. Delphine intimidates and threatens Shay who says she has no idea what Castor is and eventually cries. Delphine is stunned when Cosima tells her Shay is not the mole. Returning to Dyad, Ferdinand calls her revealing he knows Sarah is in London. Delphine agrees to meet him to discuss the leverage they have on each other. Ferdinand agrees to Sarah and Delphine's terms so they don't have Kendall killed so nobody can get her DNA. Cosima apologizes to Shay for Delphine's actions. Shay admits she was in the military but quit and lied before only to improve her dating profile. Cosima cannot tell her what is really going on so she breaks up with her.

Once Delphine discovers Krystal in Rachel's place she has Dr. Nealon arrested. Dr. Nealon admits Rachel was taken to the Neolutionists who have been manipulating Dyad, Topside and the military all along to get DNA from the original and want Delphine to join them. Delphine warns Sarah and Ferdinand of this when Nealon attacks her, showing a mutated tongue. Delphine shoots and kills Nealon who warns Delphine will be dead by morning for this. Delphine admits to Shay she was wrong and gives her a Dyad card, telling her she is a good match for Cosima and has Delphine's permission to learn everything. Delphine meets Cosima outside Bubbles. Cosima apologizes for pushing Delphine away, now understanding the hard choices she made. Delphine passionately kisses her. In a parking garage Delphine knows she is about to die and asks "What will happen to (Cosima)?"^[16] before being shot by someone unseen by the audience.

Early flashbacks reveal she moved and started studying biology specifically to help Beth and Alison. When Sarah returns, Cosima and Scott have set up a hidden lab in the basement of "The Rabbit Hole" comic shop, buying some equipment and stealing some from Dyad before they were locked out. With all their contacts at Dyad fired or disappeared they search for a cure on their own. Cosima is getting weaker and is comforted by Mrs. S over Delphine's disappearance. While investigating the implants, Kira gets angry and begins zoning out and warns Cosima she had a dream where all the other Ledas set Sarah on fire because Sarah is "changing."

Cosima is shocked to learn the truth of Leekie's demise and the Maggot-Bot the Hendrixes have. Dissecting Leekie's head she and Scott find the Maggot-Bot is still feeding on his body like a tumor and believe it is meant to change a person's DNA code. After warning Sarah, Felix brings Cosima a BrightBorn DVD featuring Evie Cho. Cosima believes the Neolutionists are creating genetically altered babies. Posing as the potential surrogate mother for Donnie's BrightBorn baby, the two go to an orientation and meet Evie Cho. Susan and Ira are also there to discuss with Evie the dental clinic death. Evie tells the prospective parents how she was born with Severe combined immunodeficiency but her parents determination and experimental treatment made her better. Evie sees Krystal con her way in and assumes she is Sarah.

Susan goes down to meet the clone and realizes it is really Cosima. Susan tells her of how BrightBorn can directly alter embryos for the best genetics though stops short of admitting that is illegal in most countries. Stealing Susan's access card, Cosima goes to the upper floors where one of the "carrier" mothers goes into labor. The baby is born with a severely deformed face. Susan catches Cosima. Susan explains that nobody asks permission to be born and these experiments are done to advance the human genome. The carrier mothers and Maggot-Bots are savage ways they have to use to advance the science without more clones to make. The Ledas and Castors are the humane way to do it. Susan knows Cosima is dying and doesn't have the resources to make a cure. She proposes the Ledas work with her and give her Kendall in exchange for find a cure for all the clones together.

Taking the deal to also free Sarah from the Maggot-Bot, she and Scott copy all theirs and Delphine's research onto a BrightBorn hard-drive for Susan. Once she and Evie remove the Maggot-Bot from Sarah, Cosima stays while Susan is to get some of Kendall's Leda genome from Scott, with Frank as Susan's guard. Asking about Delphine's fate, Evie says she was not involved with Dyad. A panicked Scott reveals the hard-drive had a Trojan on it that wiped out their copy of the data. Cosima manages to steal Sarah's Maggot-Bot off Evie's desk. Once Susan stops answering, Evie and Roxie take her to watch Kendall be killed, saying the science does not need the clones anymore despite what Susan wants. As Kendall burns, Evie tells a broken Cosima that Delphine was shot dead in the parking garage, and to tell Sarah it is over for the clones. A drained Cosima blames herself for Kendall's death and has lost hope with no Original nor data and Delphine's death. Cosima locks herself in the basement lab and cuts a hole in her cheek to implant Sarah's Maggot-Bot inside her, on the slim chance it will cure her; even if she dies her body will provide clues for a cure for the others. Scott calls Felix who convinces Cosima to stop because Krystal saw Delphine get picked up by someone after she was shot-still alive. Sarah promises to help find Delphine.

Veera is able to digitally connect Cosima with Susan, to work on a cure, though she and Scott refuse to let Rachel or Ira help. Susan is impressed with how far Cosima was able to get with limited resources. They eventually realize a Leda egg fertilized with Castor sperm could provide a cure-getting the genetics from Sarah and Ira. Cosima flies out to Susan's island with Sarah's egg to finally make a cure. Starting the blastocyst in Susan's lab it is on track to becoming a zygote. Susan lets her read about the origins of Neolution and Cosima meets Charlotte who tells her a bit about the island they are on. Cosima questions the ethics of making a young clone with a disabled leg while also knowing she could get sick. Susan says she was under pressure to continue Leda and it only matters now that they make a cure. Elsewhere, in a cabin with music and a laptop, sits Delphine; alive and well.

Flashbacks reveal Duko shot Delphine for Evie but was distracted by Krystal's cell phone. A car approaches so he flees before he can kill her. Dr. Van Lier and another man save Delphine and she is sent to the island to recover, living in the village with The Messenger. Cosima's zygote makes a gene line that can be a cure, which overjoys both her and Susan. When communication outside the island is cut off she grows suspicious and overhears that Susan is eager to start a new clone project with this breakthrough. A betrayed Cosima is locked in a room by Susan who says it's for the best to make a cure and more clones. Cosima is freed by Charlotte and steals some of the gene line. They watch and flee when Rachel stabs Susan. Cosima begins losing blood again and she and Charlotte almost freeze to death in the woods. They are taken to the village by The Messenger where she is reunited and cared for by Delphine, sharing body heat. Delphine knows The Messenger and his superior are not happy Cosima is there and did not save either of them out of kindness. But Delphine is allowed to care for Cosima. Delphine realizes Cosima has a cure and promises to use it to save her but it is not safe there, so they must keep it a secret.

Waking up the next day she meets one of the islanders named Mud who tells her she is at Revival, a village totally self-sufficient and run by the 170 year-old P.T. Westmorland who chose them from all around the world as his children. Delphine has been working in a medical clinic treating an Afghani girl with cancer, who is there for "the fountain." Delphine tells Cosima the science is real and the island is the heart of Neolution's longevity experiments. She has readied the cell line as an injection into the uterus as a possible cure. However, after the Messenger takes her to speak with Westmorland she is forced to go on a research trip to Sardinia. Hiding the cure in the back of the medical freezer she says goodbye to Cosima. Cosima watches as Rachel delivers a speech about the next stage of Neolution to the villagers. With Mud asleep outside, she sneaks into the medical trailer but decides to stay for the cure, sending Sarah away. Cosima struggles to try and inject herself, Rachel appears and does it for her, stating Westmorland chose them to make a cure together. Cosima examines Aisha the girl with cancer before being called to meet Westmorland. Westmorland claims he's lived 170 years because of his genetics and Neolution. He shows Cosima her results and that the cure appears to be working. He gives her the lab and says she can work to cure her sisters and hopes one day she will work with him in the future, though she rebuffs him. Flashbacks reveal she went to Alison's uninvited to meet her the first time at Beth's request, surprised that Alison was high at the time. On the island she is surprised when Charlotte brings her the human tooth of the monster and finds Mud lies about it even to other people at the camp. She follows Mud into Westmorland's house and sees her hooking him into a machine. Sneaking into the basement she finds pictures of wounded body parts and a bloody cell. Mud is very scared and forces Cosima out. Cosima follows her into the woods and she brings a blanket for the monster, seeing it as a feral adult man that scares even Mud. Flashbacks reveal the night Cosima and Delphine found the patent Cosima believed they totally owned her. Delphine calmed her by saying they could never own who she is as a person and promises to always protect her; Cosima promises to always defy Neolution. Scanning the tooth and finding that Aisha's tumor is shrinking she sees repeated reference to Lin 28A in a genome. Delphine returns saying she was collecting boring stool samples in Sardinia. When Cosima demands more information, Delphine snaps saying Cosima is pushing too hard and risking everything. The Messenger tells Delphine to come for a formal dinner at Westmorland which Coisma weasels into after revealing she knows of Lin 28A. Refusing to wear a formal dress she dons a tuxedo and meets with Westmorland, Rachel, Susan and Ira. Westmorland needles her about her parents, Sally and Gene; professors who love her but think she is still in school, Cosima hasn't even told them she is sick as that would reveal she is a clone and much of her life was a lie. Westmorland calls them fragile. Cosima can tell they are just manipulating, not curing Aisha's cancer but Lin 28A is real healing factor in both the feral man and Kira. Cosima is shocked when Delphine announcing she is going to Geneva next and told Westmorland that Cosima was in his basement. The feral man was a Latvian orphan named Yanis, as a boy he had a healing factor from Lin 28A being manipulated. Once he went feral, Susan tried to put the healing factor into the clones but it failed though appears to have passed onto the unintended second generation; Kira, the real "fountain" in Westmorland's plans. Delphine tells Cosima in private that she is joining Felix and Adele, they are working on the endgame but she must hide it from Cosima. Their relationship is Cosima pushing too hard and Delphine doing things to protect her without her consent, they choose to accept it, reminding each other of their promises and pledging to stop Westmorland who enjoys dividing women. With Yanis attacking villagers, Mud is sent out to look for him as bait but Yanis kills one of the hunters and breaks into Westmorland's home. Susan tells Cosima the next step is seeing if the healing factor can be passed on by harvesting Kira's eggs for 1300 surrogates Rachel's found. Mud tells Cosima she was the one who let Yanis out to spare his suffering. Yanis is in the basement with a weakened Westmorland, Yanis just wanted to go home. Cosima sees Westmorland's 170-years-old claim is a lie, he wants Kira's healing potential because he's dying and willing to make Kira into a victim like Yanis. Westmorland challenges her to do the ethical thing and kill Yanis to end his pain but she refuses to lose her humanity. Westmorland shoots Yanis himself, locking Cosima in the holding cell with his body. Locked up she tries and fails to convince Mud to let her out. Virginia Coady returns and Westmorland says it was a mistake to grant Susan's request that they be separated, the science will progress faster with them forced to work together. Susan says his mythology is cracking, he had more power when they met in the 1960s as a man but with him on dialysis he is getting weaker, his real name being John. Dr. Coady says Kira and her family will be exploited anyway and if Cosima would change her thinking, she could help set up the science's new delivery system. Cosima dismisses her as insane. The villagers of Revival begin to lose faith with one of their hunters dead and Aisha dying from her cancer. This shakes Mud even though Westmorland saved her life. She was a junkie from Seattle that was a vegetable for 6 months after an overdose, she awoke on the island and has been there ever since. Ira and Cosima convince her to help them bring down Westmorland. However he catches on and forgives Mud, telling her to go. Coady comes in with a gun pointed at Susan. Ira frees Cosima and tells her to go to the boats, giving her an envelope from Susan for protection. Cosima grabs the cure but villagers grab her, not trusting Westmorland's scientists anymore. Cosima reveals the picture in the envelope, a photo of a young Westmorland with Susan in the 1960s proving his immortality is a lie. The villagers let Coisma and Charlotte go and they sail away. The villagers begin burning everything down in front of a stunned Mud and an unhappy Westmorland watches from his mansion. She and Charlotte return to Scott and Hell-Wizard after ditching the boat. After telling Sarah and Siobhan they have a day before Kira's eggs are taken, she researches men with the right academic background who died at Cambridge in the 1960s; to find Westmorland's real identity. She uncovers John Patrick Mathieson and passes this on to Sarah. She says to Scott they can inject the cure into all the other Ledas once they find out how many are out there. Though she knows Delphine is hiding something she is okay with it and attends Felix's art opening, dancing on a painting of Rachel. After the meeting with Ferdinand and Rachel, Delphine shows Cosima all the information on the flash-drive to bring down Neolution. They upload it by clicking it together to warn the governments of the world. Cosima laughs and cries at finally being free. After the funeral, she, Scott and Hell-Wizard track the deaths of Westmorland's board. Once they realize they have Helena in the old wing of Dyad, Hell-Wizard uses his knowledge as a former security guard to sneak Scott in the main entrance posing as a doctor with an organ donation. Hell-Wizard hacks the old wing, allowing Scott to open it for Art, triggering the alarm. Scott wants to help but Art says his part is done as Art descends deeper inside.

Three months later, though they've cured clones they know like Tony and Krystal, Cosima fears they'll never find all of the Ledas in time. At the baby shower Delphine admits her guilt over Siobhan's death and that she taught Delphine how to be brave, Sarah does not blame Delphine. To rouse Sarah, Cosima admits she is scared of even holding Helena's babies noting her own lack of maternal instincts. Once the 274 Ledas are known, Cosima and Delphine end the series by travelling the world to cure them; healing Camilla in Columbia and heading to Brazil next, as a committed couple.

In the 'Classified Clone Reports By Dr. Delphine Cormier' book, released on 15 August 2017, it states in Cosima's file that she was found to be exhibiting signs of Autism Spectrum Disorder (ASD), which was picked up on by a Dyad plant at her two-year pediatric checkup but this was false, a lie to convince her parents to bring Coisma in for regular medical tests.

The character is based on Cosima Herter, the show's science consultant. Herter was a PhD student at the University of Minnesota, working on the History and Philosophy of Biology, but left the program to work on the show and her writing.^[17]

In season 2, Helena is revealed to have survived the gunshot, contrary to previous beliefs,^[18] because she is a mirror twin of Sarah, meaning her organs were formed on the opposite side of her body, including her heart, which is a rare occurrence in mirror twins. Henrik and his new group of Proletheans believe the clones are part of God's Work and should be used to understand the world. Henrik kidnaps and "marries" Helena then extracts one of her eggs and fertilizes it intending Helena to carry the pregnancy, believing that Helena's connection to Sarah means that she is the only other clone capable of conceiving a child. Helena allows Henrik to impregnate her because she wants a family. However, she learns he also implanted another of her embryos in his own daughter Gracie, and intends to do so to many other women. Helena lets Gracie and her boyfriend Mark escape and then takes her revenge on Henrik, before burning down the Prolethean's farm. Helena meets Alison and Cosima in Felix's apartment and has a dance party with them, Sarah and Kira before leaving her other eggs behind. In the season 2 finale, Helena is abducted by the military and put on a plane while Paul and Mrs. S watch.

In captivity Helena imagines a talking scorpion telling her this is a test. She is subjected to torturous "stress tests" but those are stopped after Dr. Coady learns Helena is pregnant. Helena initially disbelieves the claim Sarah sold her out and is told the military will find out how she has been able to survive so much. Dr. Coady believes she can be used as a cure for the Castor clones neurological condition if the original tissue cannot be found. Helena taunts Rudy and Paul, saying she will kill them one day. Helena manages to scout out the area and make a weapon for herself, while attempting to leave she sees the suffering Project Castor clone Parsons, giving up her chance to flee by killing him out of mercy. When Sarah arrives at the base Helena is cold to her believing Sarah gave her to the military. After learning the Castors clones are her brothers and Paul confirms the deal between the military and Mrs. S, Helena begins working with Sarah using materials around the base to free herself. However, she abandons Sarah as revenge for what she still thinks is Sarah's role in sending her to the desert base and escapes by herself. Stumbling in the Mexican desert, her imaginary scorpion mocks her as weak for regretting leaving Sarah, so she eats it. She returns to help Sarah out of the tunnels around the base. Once safe Helena says she wants to kill Mrs. S who refuses to fight her because Helena's pregnant. After hitting Mrs. S a few times, Helena is punched back once and then hugs and cries with Mrs. S as they mend things as family.

Helena is taken to live with the Hendrixes despite Donnie's protests. Helena shows Alison's daughter Gemma the canister of her eggs which she retrieved from Felix's. Helena finds Donnie attractive and likes his jokes causing him to warm up to her. Gracie also moves in and Helena is happy to see her. She doesn't blame Gracie for miscarrying the other baby and is happy to have Gracie be an Aunt to her child. Helena patches up Donnie's face and is angered when she learns the drug dealers have taken the canister as collateral until they get the pills back. Briefly posing as Alison with Donnie she gets it back and then kills all the drug dealers for threatening Alison's kids. At home she thanks Donnie for trying to protect her babies. Donnie reunites her with Jessie who loves Helena's wild side. Helena prepares to lose her virginity in Jesse's pickup truck but is interrupted by Sarah's plan.

Helena kills Rudy and rejects his claim that they are similar, him being just a disgusting rapist. She later makes a strange dessert for the dinner party. Posing as Alison with Donnie to get health care, an ultrasound reveals she is carrying identical twins, giving Helena joy. Helena finally calls Sarah to tell her the news but hopes the twins won't grow up to be like her. Two detectives come into the Hendrix home and mistake her for Alison. They are investigating the homicide of the drug dealers and went to Alison because some of her school election advertising was left behind at the crime scene. Donnie and Helena are able to deflect their questions. As Helena gets more excited about her twins, Donnie cautions her of Alison's jealousy.

The fertilized eggs in the canister have expired without liquid nitrogen so Helena buries it in the Hendrix garden and then packs up and leaves the house. Helena texts Sarah not to worry about her. Helena made a hut for herself in the woods and hunts deer for food while wearing animal pelts. Helena calls Sarah to check in, and she is unconvinced by Sarah saying everything is fine. She returns to Felix's and meets Adele. Already suspicious, Adele struggles to believe Sarah is a triplet when she, Alison and Helena are all from different regions. Frustrated Felix is concealing things from her, Helena hisses in her face though Felix is able to calm Helena down. Helena departs for the Hendrixes after learning Donnie is in trouble for the garage deaths. Felix refuses to let Adele be pulled into this and she leaves, saying real family is more than genetics, it takes honesty and acceptance. Felix is hurt by this but lets her go. Helena busts into the Hendrixes, killing Frank to save Alison. Taking the Hendrixes back to the hut, she is told to lay low for her pregnancy's sake while Sarah figures out the next move.

Hunting in the woods she sees men approach and signals a warning though they grab Alison. When Donnie tries to get to his car, a man points a gun at him. Helena attacks, allowing Donnie to knock him out but Helena is wounded with a wooden stick stabbed into her pregnant abdomen. Donnie takes her to the hospital where the twig is removed but the puncture apparently harmed one of the twins which she can sense. She is alarmed by the neonatal doctor and fears they will steal her babies' DNA. The doctor is stunned when it appears the twin's wound is healed. Helena tells Donnie she will leave and that he can only tell Sarah where she has gone. Helena stabs a needle into the doctor's cheek and escapes. She is revealed to be in a convent. Before going to the mental hospital Sarah drops in. Helena says one of the nuns there was kind to her growing up so the nun lost her tongue. Helena is writing a memoir. Sarah tells her Kira is cutting herself to find answers and Helena relates to doing that until she found her sisters. Sarah admits the instant connection Helena felt with her scared her and she felt something similar towards Kira while she was hurt on the island and believes Kira can feel the same for all the Leda clones. Despite wanting to keep Kira out of it Helena says she will have to learn about everything eventually. She suggests killing Rachel and Westmorland to keep her babies safe; they are a miracle just like she and Sarah are. On the island Mark says he can give Helena to Coady for his cure and Gracie visits Helena in the convent. Gracie lies and says Mark died two weeks ago but Helena reminds her that the twins are also part of Gracie's family. Gracie calls in to say she hasn't found Helena but Helena finds a message from Mark on the phone. Though Gracie didn't turn her in, Helena knows they will trace the phone and prepares to flee but is caught by Detective Engers. Gracie cries and says she is sorry to Helena. Engers sarcastically forgives her and executes Gracie with a shot to the head. While in transport she remembers stealing chocolate as a girl, catching a nun masturbating; for which Helena was dunked in bleach, giving her curly blonde hair and red eyes. She is locked in a room where she meets Tomas for the first time. He raises her telling her of the perverted copies, sending her out when she's older to kill her first clone in a church. Devastated they look like her, he calms her by saying she is the original and light; that day Helena began cutting in her angel wings. Mathieson is dying, needing injections and oxygen, even his hair is fake. He needs stem cells from the twins now, demanding an induced labor and C-section of Helena despite Coady saying that will damage the twins and 35 weeks is too early for them to be born. Coady complies stating the babies don't need Helena; the one who killed her sisters and stinks like an animal, mocking what kind of mother Helena would be. This shakes Helena who promises her babies that they won't be another experiment. While alone, she slits one of her wrists and prepares to die. Coady has Sarah's blood revive her. Helena manages to grab Coady with her wounded hand; attacking Coady by repeatedly smashing her head into the gurney. Sarah frees Helena as the alarm is set off in Dyad, but Helena's water breaks. Hiding in the basement, Sarah gives her a metal rod for defense and goes to search for supplies to help Helena through the delivery. Coady is wounded but determined, finding her and forcing Art to do the delivery at gunpoint. Showing Art her weapon, he tricks Coady into coming close by saying there is too much blood. He and Helena finally kill Coady by jamming the rod into her throat. Sarah and Art help her deliver two twin boys.

Three months later she lives in the Hendrix garage, temporarily calling her babies "Orange and Purple." She is worried Sarah hasn't healed from the trauma yet but happily opens her gifts at the baby shower. When Sarah finally opens up about her struggles as a mother, Helena admits she lets the boys eat sand. She shows her sisters her memoir that she's named "Orphan Black" though they think it is a dumb title. Her final scene is in the Hendrix backyard giving her sons the names of "real men who help:" Arthur and Donnie.

When Rachel hears Ethan's story, she contacts Marion Bowles who orders Leekie's death. Rachel lets him run as one act of mercy because he raised her. Upon learning the clones were designed to be infertile, her psyche begins to crack as she secretly wished to be a mother; the resulting insanity has her kidnap Kira. She admits to Ethan she cannot feel love like she did as a girl and is forced to watch as Ethan kills himself saying she does not deserve him anymore. Barely sane, Rachel convinces herself that Ethan told Sarah his cipher; when Sarah tells Rachel that she's wrong, Rachel destroys the vials of Kira's bone marrow in rage, leaving Cosima without a cure. In retaliation, Sarah shoots her in the eye with a makeshift weapon, using a pencil propelled by a fire extinguisher.

In the Season 3 premiere it is revealed the pencil gave her brain damage. Under Delphine's torture it is revealed she was working with Ferdinand to execute her self-aware sisters similar to the incident in Helsinki, this is stopped by Delphine. Now wheelchair-bound, Rachel begins various therapies with Dr. Nealon and is told Delphine told Topside that Rachel has died in a plane crash, thus confining her indoors. She begins painting to pass the time and is confronted by an enraged and desperate Felix for information on Castor. When Rachel offers no information, Felix roughs her up and mocks her saying nobody cares about her, ignoring Rachel's desire to leave. Rachel weeps while she continues painting and looking at a childhood picture with Ethan. Scott realizes her paintings may have the symbols of Ethan's genome in them. Scott is able to secretly talk this over with Rachel who reveals the symbols are a secret language she made up as a child with Ethan. Rachel will only translate the code for Sarah. Rachel demands Sarah steal Krystal's identity information for her so she can start a new life in Taiwan.

Once Rudy steals the book from Scott, Delphine is convinced Rachel told the military about it despite the fact she had no means to do so. Scott breaks her out of Dyad and has her taken to Mrs.S's house where she decodes one page of a photocopy of the book, hinting the Castor original is London. They are interrupted by Dr. Nealon, on Delphine's orders when Rachel fakes a seizure. Once her body is swapped out for a comatose Krystal, Rachel leaves the country, thanking Dr. Nealon for his help. She receives a prosthetic eye implant, while in the care of a mysterious blonde woman. Rachel wakes up with a new eye, unaware of who is keeping her now. Rachel meets Charlotte and is stunned she is under the care of her adoptive mother Susan Duncan. She and Charlotte are kept in isolation and Susan disappears for six weeks, further angering Rachel. Her new eye and physical therapy is administered by Ira, who she mocks as not being a man like the other Castors. Ira rebuffs that he's never met them and points out her little flaws like growing facial hair and needing treatment to turn her eye to a normal color.

When Susan returns, Rachel lashes out and assumes Susan failed to find Kendall again. Susan calls Rachel a disappointment. Rachel has Charlotte send online messages to Ferdinand, who agrees to help Sarah remove the Maggot Bot in his search for Rachel. Rachel is alarmed that Charlotte is coughing blood while the two talk. Susan apologizes to Rachel, saying she may be leader of Neolution one day but that she must be patient; they both must focus on the greater good of advancing human evolution. Concerned for Charlotte she theorizes immune-repressive therapy could help her since she is so young, though Susan points out that if they leave her untreated, her death could provide a way to find a cure for the clones sickness, including the Castor version. Susan leaves it up to Rachel to decide. Rachel still tries to get messages to Ferdinand through Charlotte but ultimately decides the data is more important then possibly saving Charlotte. Susan agrees but must leave her again to clean up a mess; Rachel's contacting Ferdinand. Rachel is able to get around on crutches and soon discovers she is on an island.

A defeated Susan tells her of Kendall's death and how Evie has taken over Neolution. Calling Evie to surrender, all of Neolution's backers support Evie's Maggot-Bots one of which will soon cure Evie's own Shingles. Evie will have all of Project Leda's assets transferred to her, the monitor program discontinued and leave the unaware clones alone to die of the sickness. However, Sarah and the other self-aware clones are still a threat and will be dealt with. Evie dismisses Rachel's offer to help, stating Neolution would have never given any real power to a clone, even Rachel. Rachel later tells Charlotte she is sick and will die and eventually so will Rachel. Rachel falls on her head and sees an image of a swan in her mechanical eye. It continues to haunt her and she also begins seeing an older bearded man, though Ira says her eye is fine. Her determination not to get sick and die makes her speech and walk stronger. She forms a truce with Ira and tells Susan to be honest with Charlotte.

Annoyed at Cosima shutting her out of the research, she frets over the visions in her eye, now the swan has been decapitated; but demands Susan send her back to Sarah and the others to get Susan back as the Neolution leader by working together to take down Evie, Rachel's eye looks natural, her speech is almost normal and she come move around well with a cane. With Evie about to go to the media to announce her technology which would secretly alter any children had by Maggot-Bot patients, and launch a new BrightBorn center in her failing old hometown of Tisdale; Rachel and Ira try to work with Sarah who shuts them out of finding the BrightBorn surrogates. Rachel is able to blackmail Kendra into leaving with Ira by threatening Kendra's other child. She uses Kendra and the video as a bargaining chip with Evie, saying she only wants power in Neolution for herself; not Susan or anyone else. However, Rachel's necklace is actually a camera which records Evie admitting to euthanizing and covering up the deformed BrightBorn babies. Ira sends this to the media and Rachel smugly watches Evie fall during her press conference. Rachel is still haunted by visions of the old man killing the swan at a camp. She realizes these are taking place on Susan's island and someone is trying to show her something.

Evie Cho refuses to be removed from Neolution so Dr. Van Lier kills her by activating the toxin in her own Maggot-Bot. Reuniting with Ferdinand he puts the spark back in Rachel for power while she converts him to supporting Neolution. Upon hearing Susan can make more clones, she and Ferdinand stage a coup, abandoning Ira. She meets with the Neolution board early saying Susan's plan to control evolution moved too slowly and Evie's had no proper baseline for tests. She will secure the new gene line and in countries where human cloning is not illegal, they will create many clones as test subjects for the gene-altering Maggot-Bots with these clones having no rights or freedoms as humans. Returning to the island and encouraged by The Messenger, Rachel confronts her mother. Susan says she doesn't know what she has done, Rachel's lack of restraint shows how unready she is for power and that Neolution will never truly obey her. Susan bitterly says for every good thing in Sarah and Cosima, she regrets making Rachel, it wasn't even her idea to raise Rachel in the first place. Rachel brutally stabs Susan and takes the gene line. Rachel beats Sarah with her cane and stabs her in the leg, letting loose all her hatred. She isn't fooled by Susan's threat to shoot her, as she knows Susan won't kill Neolution's Chosen Daughter. She shoots towards Sarah but misses. Sewing Susan up and putting her in the wheelchair she tells her of the visions of the swan and The Messenger in her eye. Susan says the man behind the curtain controlling all of this is P.T. Westmorland, the Neolution founder from over a century ago, still alive today. Locking Susan up and telling the board she has the science, Rachel prepares to meet Westmorland, smiling as the doorbell rings.

In Season 5, Mud says to Cosima that Rachel has been with Westmorland all day and Susan is expected to pull through. Rachel delivers a speech to everyone at Revival saying how she now sees how Westmorland shaped her whole life, Susan once stood there and advanced the science by creating the clones. Rachel will now advance it so they can all drink from the fountain. Rachel helps Cosima inject the possible cure, knowing Cosima stole some of the cell line, saying they will work together. She smugly stands over the captured Sarah. Rachel says she and Westmorland only want peace and visits to take Kira to be studied. She demands Ferdinand take a velvet glove approach and not harm the clones. She claims Westmorland has shown her the meaning of her life to map out the future of human genetics. She realizes Sarah posed as her to sneak Kira away. She is relieved when the family turns themselves in anyway, but dismisses Ferdinand for disobeying her order to be gentle with the clones. Mr. Frontenac believes Donnie is withholding Helena's location so Rachel arranges for Engers to pressure the Hendrixes, having seen Helena's ultrasound of healing embryos. She talks to Kira about the biology of the healing Spiny mouse and compares it to Kira recovering from being hit by the car. Rachel is shocked and disgusted when Alison brings her Leekie's severed head. She hated him most of her life but did not want him dead. Alison says she is free to press murder charges but the bodies of Leekie and Rudy will lead back to Neolution and her boss wouldn't like that. Rachel is forced to have Engers stand down and remove the bodies. Rachel returns to the island happy to see Westmorland. He injects her with the cure saying she deserves it the most. He snaps at her for what happened to Leekie and her suggestion he should kill the feral man. Pressuring Delphine for information on Cosima, she also greets Susan. Susan tries to say she was wrong before. While they do need her mind, Rachel presses into Susan's wound reminding her whose in charge. At the formal dinner Westmorland and Rachel needle the insecurities between Delphine and Cosima before Rachel departs. Mr. Frontenac says he let Kira stay home after she vomited on his shoes. After a call from Westmorland however, she takes Kira that night for a supposed sleep study, Siobhan warns her Rachel will need them one day. Flashbacks reveal from childhood Rachel had to recite clone tags to impress people at Dyad. As a teenager, she knew clones were becoming sick but was never allowed to see her own results and was reminded she was still part of the experiment. As a young adult, she arranged the death of the sick clone Miriam to provide data, Leekie was horrified not even sure what Rachel "was" anymore. The night she met Westmorland he praised her and called her a daughter worthy to lead; giving her a contract that freed her of her tag and monitoring. In the present she maneuvers Westmorland's board now that they have Kira. Kira gives her a friendship bracelet to bond with her. On the island she leaves flowers at her mother's grave and meets Coady. She is surprised that she must be examined by Coady to determine if the cure is working so the other Ledas may get it to control the baseline of the experiment. She sees her Dyad tag is still in her online file. She hears Westmorland talking to Fontenac about her like a monitor. Westmorland demands Kira be brought to him after he eggs are harvested and shoots her down when she disagrees. Sneaking into his office she finds his tablet has a direct link to a camera in her mechanical eye, including audio. She was never free. Returning to Dyad to prepare Kira, Rachel gets drunk, but reassures Westmorland she will do it. As she prepares the drugs she sees Kira as Rachel's childhood self. With Kira sedated she goes back to her office and receives an email from Sarah about Westmorland's real identity and that his immortality is a fraud. He can hear Rachel reject Sarah's pleas through the eye. She sends Frotenac and men to dispose of Sarah for this "false" blackmail. With her head turned away she sends a text to Art. Placing an eye-patch over the camera she sneaks Kira out and her warning allows Sarah and Siobhan to avoid the men. Rachel gives Kira back to her family. Feeling Westmorland/Mathieson trying to hack his way through the eye, she sends the email exposing him to the rest of the board and cuts out the mechanical eye with shards of a martini glass. Rachel stumbles to an elevator, and is rescued by Ferdinand. He is Siobhan's source that told her about Coady and she and Delphine are working with him to stop Neolution. Siobhan has had the others track Neolution money and knows of Neolution's evolution and sterilization plans but needs hard evidence, knowing Rachel would have kept copies of such things. Siobhan gives Rachel a flash-drive of everything they have on Neolution asking for her to complete the puzzle. Rachel and Ferdinand prepare to blackmail the board with this. Rachel says they could escape and she has a nest egg of cash for them to live luxurious lives but Ferdinand wants to build an empire. He meets with the remaining board members including Van Lier, a few have committed suicide but the rest want to go on without Westmorland. The flash-drive is empty and Ferdinand has to fight his way out. Rachel gives the real evidence to Siobhan who passes it to Delphine for it to go public. Siobhan consoles that Rachel's doing the right thing even if it is by betraying the one man who cared about her. Knowing Rachel sent him there to die, he demands to know why and she says true freedom is only when Westmorland and Neolution are powerless and Ferdinand cannot hurt her. He begins strangling her but stops himself, and Rachel warns Siobhan. Rachel tells Felix Siobhan knew what would happen, irritating him though he is thrown when he sees her wounded eye. She helps her sisters find and pressure Al-Khatib. She knows Mathieson wouldn't kill her right away, giving Sarah time to stall him while posing as Rachel. Mathieson mocks Sarah-as-Rachel saying he knows her better than she knows herself, having seen her write letters to the clones' biological mother and more intimate details.

Three months later, the day of the baby shower, she secretly meets Felix outside in an Uber. She has a glass eye, no friends and her identity has been compromised; but she is free. Though not allowed to join the group she says she has been comparing herself to the other Ledas since age six and doesn't want to see her own face again. She gives Felix the list of 274 Ledas and he wishes her a nice life.

Amelia, Sarah's and Helena's surrogate birth mother, was originally supposed to give birth to the clone raised by the Duncans.

Months later in Season 4, she has been taking self-defense classes and has made her own connection between the "twins" who attacked, her, Dyad, and BrightBorn. Using an alias to get into the BrightBorn clinic, she alarms Donnie. Cosima tells him to quiz Krystal for information. Krystal is down in the lobby stealing useless things when Donnie poses as an employee to give her a massage and interrogate her. Krystal believes Dyad is using stem cells in cosmetic surgery and attacking "healers" like herself as beautician healing self-image and doctors. Her information mainly comes from a tabloid story about a woman who supposedly had cosmetic surgery and ended up with teeth in her eyelids. When she mentions Delphine, Donnie breaks cover and mentions her real name, alarming Krystal who kicks his crotch and tries to leave. She is grabbed by Roxie who thinks she is Cosima. Susan has Krystal released since she doesn't know anything. As she is escorted out, she screams in terror, recognizing Ira's face. Krystal goes to the police station for protection and is found by Art. Once Art establishes Krystal still knows nothing of the clones, he brings in Felix, initially as a foreign detective, but she maces Felix in the eyes. Art and Felix tell her her cosmetic theory is right and to lay low, giving her an emergency cell phone with their numbers. Krystal apologizes for attacking Felix, having been on edge ever since she saw Delphine get shot. Flashbacks reveal she was following Delphine and saw Duko shoot her, Krystal's phone going off inadvertently saved Delphine's life. She sees Dr. Van Lier take her and he is annoyed Krystal is there and knows her name. In the present she sees Dr. Van Lier in front of the media during the BrightBorn scandal and calls Felix for real answers in exchange for her knowledge of Delphine and Dr. Van Lier. She meets Sarah, but in her denial sees her as too ugly to be Krystal's clone. She is correct about two sides of science fighting though she has the details wrong. Explaining what she saw, she swaps clothes with Sarah so she can go after Dr. Van Lier. However, Krystal is bored playing games with Scott and Hell-Wizard, wanting to join the real missions herself.

In Season 5, Krystal and her roommate Brie have a vlog exposing the evils of the cosmetic industry but freak out when Brie's hair begins falling out. Going to Art and Scott for help, she believes a bunch of evil companies in Switzerland did this and her contact Len Snipp, head of an ethical Bluzone cosmetic company went silent on her. Bluzone matches data from Adele and Felix and was one of the companies recently bought by Dyad, cosmetics as an industry makes more than cancer research. Getting Brie to distract Scott by flirting, Krystal sneaks off to confront Len herself, while Sarah and Art watch as her backup. Krystal truly likes Len but realizes he never actually cared about her vlog or message. When Scott realizes Brie's hair fell out due to a reaction from an experimental face cream of Len's, Krystal attacks and wrestles Len to the ground. Len says the face cream works on the cellar level and Sarah realizes it could be used to deliver Lin 28A to people. Krystal rubs the cream all over Len's beard as revenge. At the end of the series she is mentioned as one of the first clones cured by Delphine, Scott and Cosima.

Veera starred in the comic book miniseries, Orphan Black: Helsinki, which is a continuation of the former comic book series, before making her live-action debut in Season 4 of the TV series.^[20] The first issue of the comic reveals a 17-year-old Veera found out her uncle was monitoring her and used her hacking abilities to discover two other girls and tracked one named Niki Lintula down. Veera doesn't remember how she got her scars but hates them for being ugly. She is a very skilled hacker and has Aspergers Syndrome. She has been home-schooled her entire life. While the Neolutionists were trying to make more Leda clones they needed another "test subject," Dr. Dmitri decided to target Veera, her isolation minimizing the risk of collateral damage or outside complications. Left alone in the church she researches Dr. Dmitri as Ania remembered the name from her dreams. He comes in dressed as priest and captures Veera. Veera escapes with Jade, breaking a shelf of failed fetuses onto Dr. Dmitri. Taking his computer, Veera figures she was meant to be the next clone made sick to test their healing capabilities and to donate her genetics to Dyad's attempts to make more clones. Veera decides with Niki and Jade that if all the clones go to the press together they can get answers and be protected in the public eye. Unfortunately, only Justyna joins them and their intended day to reveal themselves is overshadowed by the September 11 attacks. When Justyna and Niki stop answering her calls, Veera and Jade go to Niki's school in a panic. Jade is mistaken for Veera and shot to death. Veera's Uncle Matti pulls Veera into a science lab apologizing for what he has done, saying he has a contact ready to smuggle her out of the country. The gas explosion he has rigged in the lab will serve as her cover to run. Veera flees and since the blast destroys Jade's body, Ferdinand assumes Veera is dead; and kills Uncle Matti as well for trying to say he was capturing her for Dr. Dimitri, as Dimitri and his lab were already neutralized. Veera reunites with Niki who wants Veera to flee with her family as Niki's new sister. However, Niki's family is already dead when she goes home. A horrified Veera watches as Ferdinand strangles Niki to death and prepares to burn down her house as a cover. A devastated Veera escapes. Years later, Veera wears the sheep mask to prove the Helsinki clones were not just sheep to the slaughter and will never be forgotten.

In the Season 4 premiere, the paranoid hacker "MK" is revealed to have contacted Beth, warning her not to trust Paul and of another mole in the police department. MK tries to comfort Beth after Maggie Chen is killed. In the present, she goes to Art to warn Sarah that Iceland is no longer safe, indicating that the Neolutionists are aware of their location and are coming to retrieve Kendall Malone. She was the last person Beth spoke to before her suicide, begging Beth not to leave. She speaks with Sarah when she returns; revealing Beth knew something about the Maggot-Bots and told "MK" to watch over the other clones. She flees before Sarah can meet her and avoids the paramedics. Veera has been tracking down Topside, most of whom are dead, for revenge for the Helsinki Incident, talking with a picture of Niki. When Sarah approaches for a hacker's help in finding Rachel, Veera discovers Ferdinand and is disgusted Sarah is working with him. Hacking Sarah's phone she lures him to Beth's home where she has him sit on a chair with a bomb underneath. She dunks him with gasoline intending to burn him to death for killing 6 clones and 32 of their friends and family. Veera's rage is barely held back by Sarah who convinces her not to kill him. She does however empty Ferdinand's 3.7 million dollars in his bank accounts. She coldly rejects Sarah's plea to help the other clones and leaves. After Kendall's death, Veera hacks onto Kira's computer with a message. She shows Sarah and Cosima a copy of Evie's video call stating she plans on targeting Sarah and the others. She also researches Duko for them and thanks Sarah for letting her back in. Sarah is puzzled why 'MK' wants to work with them now; Veera is revealed to have started coughing blood. In Season 5, when trying to rescue those on the island, Scott and Hell-Wizard suggest they need a hacker's help. Felix remembers how MK hacked into Kira's computer once and thinks he can use it to send a message to Veera. At the safe house, Felix sees the damage from Siobhan's fight with Ferdinand but before he can get to the laptop, a man named Mr. Frontenac forces Felix to come in for Rachel. After Felix sneaks out Scott tells him MK has reached out and is in his loft. Veera reveals to Sarah she is very sick and Rachel has started recruiting surrogates to carry new embryos. MK says she can smuggle Kira and the others away if they can get Kira out of the school. Sarah promises Scott will help treat Veera's illness in the lab. With Kira sneaked away, Felix says MK refused to leave. Sarah drives back to the loft in her Rachel disguise and is followed by Ferdinand. Veera says she is tired of running but thanks Sarah for trying to help her and she wishes things could have been different. Veera takes the blonde wig and pretends to be Sarah-as-Rachel to buy the real Sarah time. Ferdinand attacks and once he realizes it is Veera: he calls it "two revenge fantasies in one." MK spits on him for Helsinki, declaring he cannot hurt her anymore. Ferdinand loses it, both at Rachel rejecting him and Veera for robbing him. He stomps on Veera; killing her by crushing her chest. He lays the sheep mask on her body. Sarah's family and the Hendrixes both hold memorials for her.

She wears a sheep mask in public to hide her identity. The mask resembles Dolly, the first successfully cloned organism. This has led to her being nicknamed "Dolly" by fans in addition to her chosen pseudonym of MK.^[21]

After hiding with Gracie and consummating their marriage, he confesses he is still in the military and was sent to collect some genetic samples her father apparently stole. Gracie tries to get them back from her father's friend Willard Finch, but all he gives her is apparently useless files. Gracie seems to return to her mother once learning Mark is a clone. Mark tortures Willard who dies of a heart attack. Mark is enraged Sarah told Gracie he is a clone. Sarah also reveals to Mark that he and his brothers are in fact genetic brothers to the Leda clones, a fact determined by Cosima's autopsy of Seth. Mark rejects them as his family. While trying to leave, he is shot twice by Gracie's mother Bonnie: once in the leg and once in the torso. Sarah helps him to escape from the cornfield in which he was shot, bringing him to an abandoned house and removing the bullet from his leg with a pair of pliers. He supervises Sarah as she unearths the corpse of Henrik's son, Abel, who died as an infant. The baby's DNA is believed to have been replicated from the Castor genome. After pacifying an altercation between Sarah and Rudy, he recovers the boxed corpse and states his intentions to relinquish it to the military for examination, along with Rudy and an unwilling Sarah.

Meanwhile, Gracie is taken back to the Proleathans but rejected again after she suffers a miscarriage. Mark is revealed to be Rudy's superior within the military. Back at the desert base Dr. Coady praises his work at getting the DNA and has his arm tattooed again. Mark claims he burned it off and married Gracie only as a cover. Dr. Coady reminds him his bond with Gracie wasn't real, and has Mark log Gracie into a journal of his sexual encounters as is regulation for the Castors. Meanwhile, Gracie seeks out Art who brings her to Mrs. S and Felix. Mrs. S bonds with her by telling her how her husband died in a bar fight. Gracie is eager to get away from her sheltered life, trying alcohol and dancing with Mrs. S and Felix but then suddenly having immense pain and sickly red eyes, a disease apparently infecting everyone who has sex with a Castor clone. Gracie's eyes clear up, and she is examined at Dyad by Delphine and Cosima.

Mark formally meets Paul at the desert base, previously being unaware Paul was involved in Castor. After they discover the infection of the Castor clones' sexual partners and Dr. Coady's tracking of them, Mark warns Paul that Rudy did not return with his patrol and someone called him, making Paul realize the director of the military program is supporting Dr. Coady. Gracie overhears Mark and his brothers are dying of a sickness. After staying at Alison's house briefly, Gracie says goodbye to Helena and calls Cosima to apologize. She was the one who told the military about Ethan's book to save Mark. She is reunited with him thanks to David Benchman. Mark and Gracie hide in a hotel wanting to spend their time together before Mark gets sick and dies. Sarah is able to convince him Dr. Coady won't let him be free and he should help the Leda clones. He does so, allowing them to prepare Alison for Rudy's arrival. Mark poses as Rudy in a video call to Dr. Coady telling her where to find Kendall. Dr. Coady takes the bait and is captured by Ferdinand as part of Sarah's plan.

In Season 5 he is brought to the island under the guise of Coady's prisoner, but reveals he reached out to her for a deal. She will cure him and he can provide her Helena. He is surprised when she demands an ejaculate sample. Taking him to Ira's grave, Coady confesses that Mark is the only Castor left and she drew straws when deciding which Castor to give Susan. He calls Gracie at the convent, though Gracie lies that she hasn't found Helena yet. Coady sees through this. With Helena captured, Coady lies and says Gracie will rejoin them after the twins are born. John orders Coady to kill Mark even though he is the last Castor, they have his pathogen and need to cut loose ends before moving into the future as he did when he ordered Gracie's death to force things along. Although Coady is conflicted, she administers a lethal injection to Mark, calling it the cure. Mark feels drowsy as he says Gracie wants to be a dental hygienist, and he wants to be a teacher. Coady tells him to nap and then he'll be closer to seeing Gracie again when he wakes up. Mark thanks his Mom, unknowing and feeling happy, passing away in his sleep.

In Season 5 Ira is with Felix and tells Sarah how to find the boat and the village is called Revival but says Susan would never speak of it, to Felix's exasperation. Ira is forced to be watched by Scott and Hell-Wizard. Once Ira learns Rachel stabbed Susan he promises to side with Felix. When Rachel comes for Kira, Felix wishes Ira luck back on the island. Susan wakes up on the island, surprised that she is still alive though happy to see Ira. She knows Percival Westmorland must need her alive for something. She agrees with Westmorland's vision but not his methods. She tells Ira that before they found Kendall Malone and started the clone project Westmorland had her work with Virginia Coady who Susan considered too ruthless. After they damaged the boy with the special genome Westmorland separated them; Susan took Leda and Virginia took Castor. After Project Castor fell, Susan had Virginia committed to a mental hospital and hid her from Westmorland. Susan knows he needs her scientific mind to deal with the Kira breakthrough and requests access to all of Rachel's data on Kira. Westmorland agrees but says Rachel is in charge. Susan tells Ira she is prepared to lie to Westmorland to protect themselves. Reunited with Rachel he sarcastically comments he hid the knives. He attends the formal dinner subtly hinting to Cosima he is on her side. As Cosima leaves to confront Westmorland, Ira babbles about a red roof, the start of his glitching. When Coady returns to the island, Ira desires to learn about himself from her, Susan slaps him and his glitches get worse. Coady claims she is close to a Castor cure as Ira watches her take blood from a healthy boy. Coady remembers that Ira screamed at age four when taken from the other Castors. Susan says Coady is a liar and is shocked and disgusted Westmorland is using children's blood trying to extend his life. Susan gave her soul to Neolution but now says it is time to burn it all down. Cosima and Ira convince Mud to help them though Susan is caught trying to poison Westmorland's dialysis treatment. Ira lets Cosima out of the cage to go to the boats and gives her the envelope from Susan as protection. Ira returns to the house as his nose begins to bleed, finding Susan dead from the poison on the balcony. He sits next to her as he weakens. He is confirmed dead when Mark returns, buried next to Susan.

Despite their romance, he still calls Susan "mother" while others are present.