With Helena forced to take shelter behind enemy lines, it’s a bloody last stand for survival as Sarah and Art struggle to protect her, and end the siege on the sestras once and for all.

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.

Mrs. S orders the sisters to take a night off from sleuthing to celebrate Felix's art opening. But while Felix attempts to impress a famous gallerist with the help of his sestras, Sarah remains on edge with a nagging suspicion that S is hiding something. Meanwhile, 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 P. T. Westmorland demands a more aggressive action on Kira, and Sarah fights to save her daughter, Rachel discovers a dark secret that makes her question her place within Neolution. Meanwhile, Cosima has returned with a vital clue to Westmorland's true identity.

Cosima is forced into an alliance when an old enemy returns to the island, accelerating P. T. Westmorland's sinister agenda. Meanwhile, on the mainland, Krystal stumbles onto a vital clue to the Neolution endgame. Sarah and Mrs. S’s research into Neolution's corporate ties leads to the cosmetics industry and an inevitable cross with Krystal Goderitch. But before Sarah can dig deeper, Krystal hijacks the investigation.

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, causing a dangerous showdown with the Neolution patriarch.

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 discovery more terrible than she could have ever imagined. As more pieces slide into place, the puzzle only seems to become more complicated.

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.