Castor and Topside force Sarah to make uneasy alliances. But there is some rest for the wicked, when Donnie gives Helena an unexpected ‘gift’, and the results of Alison’s candidacy finally come in. Even as team Leda takes a moment to breathe, change is afoot and a life hangs in the balance.
Rachel wakes up in what seems to be a luxurious bedroom, but there is nobody there. A letter she finds advises her to remove the bandage over her the socket of her ruined left eye, and she finds that she has a working artificial eye.
Art has found an industrial space that nobody is using, and Scott sets it up as a bio-containment area. Sarah and Siobhan install Kendall Malone there; she is fussing and complaining all the way, chain-smoking as always. They are concerned that none of Kendall's DNA get lost, to be collected by enemies. Sarah remarks how Kendall doesn't look like her, and Scott explains that's how it is with chimeras, the two cell lines express differently. Siobhan is still quite hostile to Kendall, ready to kill her, and incinerate her, or dissolve her in sulphuric acid, on any chance of Kendall's DNA being lost.
Virginia Coady meets with officials in a U. S. government building, she says the program is still viable. Rudy is there as her guard, showing further signs of the Castor neurological problem. Coady sends Rudy to the only unprotected member of Sarah's group, Alison.
It's election day for Alison, and she is campaigning, with a campaign bus to carry supporters around. At home, Donnie gives Helena a present: he leads her to her boyfriend Jesse, and they are glad to be reunited.
Cosima meets with Shay again, but Shay is still unnerved by the visit from Delphine. She defends her "fluffing" of her dating profile, as that's just what people do, and for that matter she doesn't really know what's up with Cosima, Cosima won't share.
Ferdinand and his henchman visit Delphine at Dyad; Ferdinand didn't find Kendall or her DNA, only her burned-out house. He still wants the Castor original, and Delphine says there's a different deal: Sarah is there with her. (The last time Ferdinand was in Toronto, he and Rachel played with sex together, but Sarah uses enough of their suggestive talk together for him to realize, it wasn't Rachel that last time, it was Sarah.) Sarah offers samples from Kendall, so Topside can duplicate the Duncans' cloning work, but she wants the Castor program dead.
Sarah and Felix find the hotel where Mark and Gracie are staying, and they agree, Virginia Coady isn't interested in a cure to the Castor problem, she just wants the biological weapon they are. Mark just wants a few months together with Gracie before he succumbs, but he and Sarah have an idea of how to stop Coady for now.
At the industrial space, Kendall and Siobhan renew their hostility, over how Kendall killed John, Siobhan's husband, and Siobhan will be glad to kill Kendall.
In the Dyad medical facility, we see Rachel, bandaged and unconscious. Delphine tells Dr. Nealon to move her to another facility, so Ferdinand doesn't find her (he thinks she's dead). After Nealon leaves, Rachel wakes, and she's not Rachel, she's Krystal, the clone from the nail salon, who has no idea where she is why she's here. Delphine tries to understand what's gone on.
Helena and Jesse are making out, when Helena gets a call on her clone phone: her family needs help. Rudy (experiencing flashes of neurological trouble) has arrived at the polling station Alison and Donnie are at, and they arrange for Rudy to follow as they drive the campaign bus to the Hendrix house. There, Alison gets out and goes in the house, which encourages Rudy to go in through the garage door, where he finds not Alison, but Helena. They fight; her ferocity is a match for his strength, along with his neurological problems, and she beats him to death.
Sarah and Felix bring Mark to the industrial site with Kendall. They check in with Donnie, who says Rudy is in place. Mark braces himself, and Sarah repeatedly punches him in the face. Mark (with a hood obscuring his lack of a scar) pretends to be Rudy, bloodied and bruised, and calls Dr. Coady, telling her he got to Helena (hence the bruises), and she led him to Kendall; he turns the phone to show Kendall there. He sends Dr. Coady a location, and says he's there.
Dr. Coady and troops arrive at the location. While the troops are away, Ferdinand comes, kills Dr. Coady's driver, and tells her she's been tricked, there's nothing here. Nothing further is shown of her fate in this season.
Sarah and Siobhan agree that the Castor program is now no longer an active enemy. They get Kendall to explain that, years after she donated her cell lines, Ethan Duncan came to her and said Neolution had ruined the science, and corrupted his wife Susan, and he was on the run, so Kendall sent him to her daughter Siobhan, the rebel who had contacts, and in return Ethan steered one clone that wasn't under "their" control to Siobhan as a foster daughter: Sarah.
At Dyad, Delphine has Dr. Nealon, restrained and with guards near; she's learned that the real Rachel went to Austria, then to a private hospital, then disappeared. Nealon says that Neolution is running all of this, Dyad and Topside, Dr. Leekie was a useful face, but Neolution is much more than his ideas.
At the industrial site, Ferdinand and his henchman arrive, and Sarah leads them to Kendall, to get the arranged blood sample.
Dr. Nealon tells Delphine that Topside will soon deliver the genome into the hands of Neolution. He then bites his cheek, chews a bit, and jumps at her, he was handcuffed but not really restrained, and she had no guards in the room, he tries to spit something into her mouth, when she shoots him. She examines, and finds that he was trying to spit what looks like a worm. He lives long enough to say that Delphine won't live until morning.
Ferdinand's henchman has collected Kendall's blood sample, when Delphine calls Sarah to tell her to stop, the sample will get to Neolution, Ferdinand is only their pawn. Delphine also tells Ferdinand that Rachel is alive. He puts a few things together, turns and kills his henchman, though the henchman boasts that Neolutionists are everywhere. Ferdinand says never mind Kendall's genetic material, he's the enemy of Neolution and therefore Sarah's friend, so they should take Kendall and run away somewhere.
At Bubbles, there is a celebratory dinner, Sarah, family, and all the sestras. Alison has won the election. They toast missing ones, such as Beth.
Delphine parks in the Dyad parking floor, realizes she is being followed, turns and asks someone we don't see, "What will happen to her?" There is a gunshot and she falls. Footsteps approach her.
Rachel is in her room, and a door opens, it's young Charlotte Bowles, and an elderly blond woman, Susan Duncan, Rachel's mother.
We see a snow field, and a lone house, with Kira walking outside. Two snow speeders zoom to the house, and Kira smiles and runs to them. The first speeder driver takes off her mask, and it's Sarah.