When terrifying evidence suggests the Orphans are part of a sinister ongoing experiment, Sarah’s suspicions turn to Paul, Beth’s boyfriend. But her probing inadvertently triggers Paul’s own investigation, bringing him dangerously close to the truth. Meanwhile, paranoid Alison piles on a whole new level of complication.

After Kira’s life is threatened, Sarah is on the warpath, but Dr. Leekie makes her think twice about her plans for revenge. Meanwhile, Cosima faces the truth about Delphine, forcing her to choose sides. Now, it’s up to Sarah to decide the killer’s fate, but the truth about where Sarah came from changes everything.

After hitting the road with Felix, Sarah is forced to turn to a ghost from her past - an old flame named Cal Morrison. When their brief respite is brutally shattered, Sarah realizes that no matter how far she runs, it will never be far enough.

Cosima takes a turn for the worse, forcing Sarah to take desperate action which results in tragic consequences for those she loves. The Proletheans set their ultimate plan in motion, while Alison and Donnie tangle with the law.

Helena and Sarah are reunited at the Castor camp. As Sarah suffers testing, Paul appears to chide her; but his allegiances are beginning to strain. While the Leda family worries about Sarah’s absence, Gracie ‘breaks loose’ under the care of Mrs. S and an unwilling Felix. Cosima falls hard for an internet date, Shay.

Sarah realizes her goals have aligned with her once enemy and forms a precarious alliance in hopes of getting to the head of Neolution. Meanwhile, on her end, Alison dispatches Felix and Donnie to infiltrate a Neolution fertility clinic that Beth investigated. Back at the lab, Cosima and Scott receive a revolting delivery from Alison. As Rachel grows closer to Charlotte, Susan Duncan leaves a devastating decision in her hands.

With Susan Duncan deposed, Sarah finds herself in the same position as Rachel — under the heel of a new HBIC — causing the archenemies to come together for the greater good. Cosima and Susan butt heads on the ethical implications of human experiments. Meanwhile, when the Hendrixes' legal counsel, Adele, further investigates Donnie’s case, she begins to suspect Felix is keeping deep secrets. Helena’s arrival forces Felix to make a difficult decision.

Stuck on the sidelines with Neolutionists crawling all over her home, Alison seeks to return to her community center, but Bailey Downs has moved on from her. As she flounders to take back some semblance of control, the ghost of friendships' past rears its handsome head. Art and his new partner show up at the Hendrix residence to continue their search for Helena, forcing Art to make a difficult moral judgement.

A devastating loss is eclipsed when word reaches Sarah that Helena has been kidnapped. Clone Club bands together in a race against time, determined to find her before she has her babies. And with time running out, Sarah is forced into action in a last-ditch effort to save her sestra.