Olivia begins to regain her memories of her encounter with William Bell. Meanwhile, the "First Wave" tries to collect the head of their leader, and the traitor makes his move.

The First Wave breaks into a mental hospital and cures a long-term patient suffering from schizophrenia. When the Fringe team investigates, Olivia discovers that the group's leader has one of the heads stolen from cryogenic storage months earlier. Meanwhile, two other mental patients are cured of their schizophrenia and the team soon realize that something was taken from each patients' brain... and Walter holds the key to realizing what First Wave is after.

Two teenagers turn up dead and evidence indicates that shapeshifters have borrowed their forms for some special mission. While the Fringe team tries to track them down, Peter grows increasingly suspicious of Walter's secretive behavior.

In Noyo County, Washington, Peter stumbles across a grisly murder with ties to Newton and First Wave. He is forced to team up with a suspicious sheriff to get to the heart of the case. Meanwhile, Walter has trouble functioning without Peter, and worries he will be sent back to the mental institute.

The story alternates to the Fringe Team "over here" where they investigate a mystifying case that people are discovered in a trance-like state that ultimately leads to their death. The unlikely suspect: a mysterious box. As Peter and Walter collaborate to study its properties, alternate Olivia presses on and turns up the heat on an unsuspecting Peter. Meanwhile, key information about the future is revealed when Walter and Nina meet at Massive Dynamic for the emotional reading of the last will and testament of William Bell.