Season synopsis
Contains spoilers for this season and earlier seasons.
Olivia is trapped in the parallel universe while Walternate’s team conditions her to believe she is Fauxlivia. Meanwhile Fauxlivia, now living among the prime-universe team, helps Walter and Peter investigate the paired Wave Sink devices and grows close to Peter. She becomes pregnant by him. Olivia breaks through her conditioning long enough to cross over during a Cortexiphan test and ask a cleaning woman to warn Peter that she is trapped in the other universe. Her escape is aided by alternate-universe Broyles, who is killed by Walternate’s agents; Fauxlivia is recalled to her own world.
Back in the prime universe, Olivia and Peter struggle with the betrayal before reconciling and admitting their feelings. The team learns that the two devices are linked and that Walternate intends to activate his machine to destroy the prime universe, hoping to repair the damage Walter caused. Walternate secretly accelerates Fauxlivia’s pregnancy so he can use the baby’s blood to power the device. The resulting activation destabilises both universes. Walter and Peter work with Sam Weiss to understand the machine, while Walter fears that the Observer’s intervention in Peter’s childhood has set a chain of events in motion.
Peter enters the machine and wakes in 2026, where the parallel universe has been destroyed and the prime universe is now collapsing too. Walternate kills Olivia in revenge, while Walter is blamed for the catastrophe. After confronting the future’s consequences, Peter returns his awareness to the present and uses the machine to create a bridge between the universes. He asks representatives from both sides to work together to prevent their destruction. Peter then vanishes from everyone’s memory and from the room; the Observers note that the others no longer remember him.