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.
After witnessing a woman's suicide, street-wise chameleon Sarah assumes the stranger's identity, who happens to look just like her. Expecting to solve all her problems by cleaning out the dead woman's savings, Sarah is instead thrust headlong into a kaleidoscopic mystery as she realizes the dizzying truth: she and the dead woman are clones.
As Sarah searches for answers, she discovers the chilling fact that there are more people like her out there - genetically identical individuals who were planted in unsuspecting birth parents and nurtured in completely different circumstances. With no idea who created the clones, she'll need to discover the reason in a hurry as an assassin is killing them one by one.