Season synopsis
Contains spoilers for this season and earlier seasons.
Olivia returns from her meeting with William Bell badly injured and unable at first to recall his warning. Fringe Division faces closure while Broyles argues to keep it operating; meanwhile, a shapeshifter replaces Charlie Francis and searches for a device hidden in frozen heads. Olivia’s memories return in fragments, and the team’s cases increasingly point to breaches between the two universes. The shapeshifter operation is led by Thomas Jerome Newton, whose agents are preparing a coordinated crossing.
Walter eventually tells Olivia that Peter is the alternate universe’s son he rescued as a child. Walter’s own Peter died, and after Walternate failed to notice that his experiment had produced a cure, Walter crossed over and brought the other Peter home. September, an Observer, distracted Walternate at a crucial moment; Walter’s crossing damaged the other universe and set the two worlds on a collision course. Olivia also discovers her childhood Cortexiphan trials and reconnects with other subjects, whose abilities help open a passage when Peter is taken back across the divide.
On the other side, Peter learns that his biological father, Walternate, intends to use him to activate an ancient machine linked to both worlds. Olivia and Walter cross over to retrieve him, aided by the Cortexiphan subjects and Bell, who is already living there. Olivia reaches Peter, and the group tries to escape before Walternate’s forces can stop them. Bell sacrifices himself to power their return device. Fauxlivia, Olivia’s counterpart, captures the returning Olivia and takes her place on the journey home; the real Olivia is left behind in the parallel universe. Peter returns with Walter, unaware that the woman accompanying them is not Olivia, while the two worlds’ conflict remains unresolved.