In an attempt to protect Amy, Wolgast convinces Sykes and Lear to let them outside of the facility for exercise. As emotional flashbacks reveal Carter's life leading up to his death-row sentencing, Fanning's hold on those kept inside Project Noah grows stronger. Meanwhile, the virals gain power over the facility's staff, leading Richards and Wolgast to reunite so they can take down a rogue soldier.

When the only way to stop Fanning and the virals' escape from Project NOAH involves a dangerous explosion that could leave Brad, Sykes, and the cure for the virus caught in the crossfire, Amy must be the one to decide what's best for humanity. In the wake of this, surprising alliances form and a key figure returns to instill confidence, convincing everyone to fight for their lives.