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.

The arrival of a building from the alternate Earth causes massive death and destruction to those occupying the site at its arrival. Walter soon realizes that to equalize the balance between universes, another building will have to disappear... along with everyone inside it. The team's only chance is for Walter to activate Olivia's long-buried ability to distinguish objects from the other universe.

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.