While Alison struggles with Aynsley's death and Cosima grapples with the worsening symptoms of her mysterious sickness, Sarah enlists Art’s help to find Kira and is shocked when she learns where the trail leads.

Sarah comes home looking for answers, and with the help of Cosima, they begin digging into the origins of the clone experiment. The hunt for answers takes her right into the belly of the beast, but getting out could cost her more than she knows.

A new player in the clone conspiracy turns up at Felix’s door, sending him into crisis mode. With Cosima running out of options, Sarah struggles with the decision to surrender a crucial piece of leverage and make a deal with Dyad.

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.

After evading a Neolution attack in Iceland, Sarah returns home to track down an elusive new ally. As Cosima struggles with Delphine’s disappearance, Alison and Donnie host a pregnant and ever-hungry Helena. Meanwhile Felix, feeling like an outsider, embarks on his own journey of self-discovery.

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.

When Cosima admits doubts about finding a cure in time to save her life, Sarah makes a lone decision that exposes Kendall to those she’s spent years hiding from. Meanwhile, Art and Felix team up to protect naïve clone, Krystal Godderitch, from herself.