When fractures within the Synth community start to appear, all hope of stability comes under threat, and both families are brought back to fight for the Green-Eyes' survival.

A grieving Max must face the consequences of his painful decision. Laura discovers she's not being told everything at the Dryden Commission, while Joe uncovers Karen's shocking secret.

As Leo struggles to come to terms with being human, Mattie takes him back to the Hawkins' home, where a surprise night out allows them to confront their feelings for each other. Laura is determined to uncover the truth about the too-secret Operation Basswood and tries to enlist Dr. Neil Sommer's help, only for things to take an unexpected turn. Joe reluctantly decides to help Karen with Sam, and Niska receives a mysterious message.

Laura leads a tense Dryden Commission on a visit to the Railyard, but will Agnes' anger threaten its success? Mia comes face to face with Ed forcing her to confront her past, while an evening out for Karen, Sam and Joe turns to tragedy.

While Sam reels from the events of Waltringham and Joe struggles to help him through it, truths are revealed and dangerous plans put into action at the Railyard.

Laura reels from her heartbreaking decision. Niska's journey takes an unexpected turn. And Leo races to be by Max's side, but walks into danger.

In a dramatic showdown, humans and Synths go head-to-head - but will Mia and Max's peaceful protest cost them their lives? Laura, Niska and Mattie face major decisions.