A man in Seattle goes berserk, attacking his boss and claiming his victim is a demon. After the killer dies of what appears to be exhaustion, the Fringe Division discover it's only the first in a series of killings where the persons initiating the attacks were in a dreaming state while awake

A state trooper picks up a runaway boy, but when he undergoes a strange transformation, three murders result. The Fringe team is called in to investigate and discover that a small town harbors a horrible secret.

Walter explains to Olivia how Peter came from the alternate universe, and how he was willing to risk everything to save his son.

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.

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.

The alternate universe Fringe Division investigates a shocking breach of security when a twin frees his brother from a quarantined Amber area. As the team sets out to crack this sophisticated case, Walternate experiments over there more with Olivia as she reenters the tank. Meanwhile, visions of Peter continue to haunt Olivia about returning to the “other side”.

When the Fringe Team visits Massive Dynamic’s assembly of the doomsday device, Walter becomes greatly concerned for Peter’s well-being, so he turns to Nina for added brain power to understand the relationship between Peter and the superweapon. Meanwhile, the discovery of a dead body triggers an intense investigation.

The Fringe Team investigates a group of thieves who can break the laws of gravity. Meanwhile, Walter attempts to delay the damage he's caused to the fabric of the universe.

The beginning of the end is triggered when Walternate finds a way to wreak havoc “over here."