Desperate to get off the island and reunite with her family, a wounded Sarah journeys into the island's interior, only to discover a mysterious village - the beating heart of the Neolution agenda.

Dragged home from the Island by Neolution, Sarah refuses to follow Rachel's new regime. Sarah sets a plan in motion to get her and her daughter out of Neolution's reach for good.

As Clone Club reels from the loss of one of their own, Sarah gnaws at the shackles Rachel has firmly placed around her family. Alison struggles to find her place in the sisterhood.

Sarah and Siobhan follow a lead on a Neolution defector, hoping for enough leverage to free Kira from Dyad's clutches. Also, Cosima investigates rumors about a creature in the woods.

While Sarah and Kira spend time at home bonding, Cosima unlocks the island's biggest secret, discovering a link between the village's so-called creature and the science around Kira.

Cosima is forced into an alliance with Susan Duncan when an old enemy returns to the Island. Meanwhile, on the mainland, Krystal stumbles onto a vital clue to the Neolution endgame.

As Westmoreland demands a more aggressive approach with Kira, and Sarah fights to save her daughter, Rachel discovers a dark secret that makes her question her place within Neolution.

Now that Sarah and Mrs. S have Kira back, they need to get her into a safe place. The activity around their house is remarkably quiet which Sarah believes is not a good sign. However, Mrs. S would like them now to focus on other things in their lives, namely Felix's first art exhibit in two years, he and Adele who have come back from their sleuthing in Switzerland. This exhibit is important for Felix as major art dealers and critics will be in attendance. All the sisters who are around - Sarah, Alison and Cosima - know the role they are to play in Felix's big day. However, Sarah can't help but believe that Mrs. S is up to something. Cosima can't ask Delphine, Mrs. S's recent partner in crime, in their new "don't ask, don't tell" relationship. If Sarah were to discover what Mrs. S and Delphine are up to, she may not agree with what they hope will be their final attempts to bring Neolution down for good. Meanwhile, Gracie is still at the convent with Helena, the latter unaware of Gracie's true purpose for being there, which is not a need for sanctuary following Mark's death.

Sarah, Felix and Kira mourning the death of S coincides with them and the other sisters learning from Sister Irina that Helena has been kidnapped. The sisters' first thought is that she has been taken to the island, but they figure that the one person who they now may seemingly be able to trust to some extent who would know for sure is Rachel. Rachel is only able to fill in some of the pieces. However, with news of Dyad's involvement in the genetics project hitting the media, Interpol has been called in to take over from the police the investigation of the deaths of some Dyad board members. While this may pose some problems for Art, he knows that Enger too is someone who probably knows Helena's whereabouts. The sisters also believe that Al-Khatib may be useful under the current circumstances, where he is trying to protect himself from what is going on with the Board. Meanwhile, Westmorland is becoming more desperate for a cure as he knows he is close to death without it. He orders action be taken on Helena earlier than she may be ready. Under this circumstance, Coady, as the lead scientist, has to decide where her priorities lie: still with Westmorland, to Mark as the remaining Castor, or to the actual science. And as action is taken upon Helena, she has her own thoughts about what is best for herself and her unborn children, taking into account her entire existence, where she long believed she was the original and now knows she is only one of the clones.

Now in labor, Helena is forced to hunker down in the basement of Old Dyad for the delivery. It's a cage match for survival as Sarah and Art struggle to protect her in a desperate last stand against Neolution.