Sarah is deeply wounded and struggling to stay alive on the Island. Driven deep into its forest by Neolutionists and worse, she strives to make it far enough to rescue Cosima. Meanwhile, a recovering Cosima reunites with Delphine, but there's way more going on this Island than Cosima imagined and Delphine can't give her all the answers she needs. What is clear is that Rachel is now in firmly in charge at the right-hand of the 170-year-old founder of Neolution, PT Westmorland. Back home, Neolution puts the screws to Alison and Donnie in their hunt for Helena. The sestras couldn't be further apart when they need most to be together.
Captured by Neolution Sarah receives a damning ultimatum from Rachel: come into the fold, or lose your family. Her decision causes a clash with Kira who begins exploring her own maturity. Meanwhile, Ferdinand struggles to get a handle on Rachel's new velvet glove mandate in pursuit of the clones. With Neolutionists and Ferdinand watching their every move, Felix brings an old ally into the mix to help his family get Kira to safety. On the Island, Cosima struggles to comprehend the reality of the Neolution myth made real.
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.
Following up on intel from a mysterious source, Mrs. S heads on the road with Sarah to investigate a lead on a Neolution defector. Meanwhile, an unexpected reunion takes place on the island, while Cosima's research leads her to a terrible discovery.
While Sarah and Kira spend some well-needed bonding time at home, secrets are unlocked about Kira's special gifts that are surprisingly linked to the island's creature. Meanwhile, Cosima joins Delphine at the mansion for a twisted family dinner.
Cosima is forced into an alliance with Susan Duncan when an old enemy returns to the island, accelerating P.T. Westmorland's sinister agenda. Meanwhile, Krystal stumbles onto a vital clue to the Neolution endgame.
As P.T. Westmorland demands a more aggressive approach with Kira, Rachel discovers a dark secret that makes her question her place within Neolution. Sarah fights to save her daughter.
The sisters take a night off to celebrate Felix's art opening. Wounded and desperate, Rachel reunites with an old ally, but their plans for revenge on Neolution put clone club in the line of fire.
As Sarah reels from a painful loss, she's dealt another blow: Helena has been kidnapped. The sisters band together in a race against time, determined to find Helena before an unmasked and unhinged John Mathieson lays hands on her babies.
Helena takes shelter behind enemy lines, and Sarah and Art struggle to protect her and end the siege.