Olivia dreams about a suicide as the event really happens at Grand Central Station; shocking information about the Z.F.T. manuscript is revealed.

An amnesiac Olivia makes her return from the parallel universe, while Walter, Pete, and Junior Agent Amy Jessup investigate the mysterious death of a man found with puncture holes in his palate. Meanwhile, Broyles defends the Fringe Division from a Senate subcommittee threatening to shut the organization down.

When Walter discovers that Peter has traveled to the alternate universe, he and Olivia gather three cortexiphan children with the ability to transition safely between the two Earths.

Walternate asks Peter to help complete the device, while the fugitives Walter and Olivia are reunited with William Bell. Meanwhile, the alternate world's Fringe Division closes in on the invaders, and Peter must make a life-shattering decision.