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

When the passengers on a commuter train all die instantly of massive power loss, the team realizes that a time traveler is responsible... and that it may be impossible to apprehend him. Meanwhile, Walter writes a letter to Peter explaining his origins.

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.

Peter struggles to cope with recent events; Olivia searches for an ally; a device that communicates between universes is discovered...

As the thrilling third season propels to a climactic close, questions will be answered as Peter confronts his destiny and a beloved team member meets an untimely demise.

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.

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.

The Observer chooses to do something other than observe, abducting a college student. However, when the Fringe team investigates, they discover that there is more than one Observer.. in both time and space.

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.

As devastation spreads on This Side, Walter, Olivia, and Sam Weiss struggle to find a way to stop the destruction and discover that one individual has the ability to allow Peter access to the Machine.

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.

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.

After the extraordinary turn of events that shockingly left an imprisoned Olivia "over there," she fights to find her way home. Meanwhile, Peter and Walter try to move on with their lives unknowingly alongside alternate Olivia.

When a serial kidnapper “over there” strikes again, the emotional and familiar case hits home for Colonel Broyles, sending a determined Olivia to uncover additional details about the abductions. In the meantime, Olivia fights on and reunites with Henry to enlist his services on an intense and covert mission to return home.

In an effort to remove Bell's consciousness from Olivia's mind, Peter, Bell, and Walter enter Olivia's subconscious and attempt to find her personality, which has hidden itself somewhere safe.

The Fringe team engages a desperate plan as Olivia embarks on a dangerous and otherworldly journey into the unknown. Then, Peter, Olivia, Walter, Astrid and Broyles face off against the Observers in one final and extraordinary battle for the fate of mankind.

In this case, timing is everything as a series of anomalous events lead the Fringe Division to investigate deadly incidents with unimaginable coincidences. As the freaky crimes continue to occur, the team is in a race against time to protect potential victims. Meanwhile, Secretary Bishop shares his strategic plan with Colonel Broyles as Olivia grapples with a heart-stopping vision.

An Observer makes contact with the Fringe Team to help rectify a mistake. Meanwhile, Walter befriends Roscoe Joyce, keyboardist for Walter's favorite 1970s band, "Violet Sedan Chair." Walter will learn the real reason the band broke up, and realize that the lives of these two men, who have never met before, overlap in strange and unexpected ways.

In a follow up to last season’s “Peter” flashback episode, the all-new “Six Months Later” episode revisits a poignant period of time for both the Bishops and Olivia.

The teams on both sides fight on for a common cause, and there are shocking developments tied to the Cortexiphan children.

Setting the stage for the dramatic and revealing first season finale are a sudden and unexpected attack on someone with close ties to Fringe Division, the return of bioterrorist David Robert Jones and the inexplicable disappearance of Walter. Find out more about the mysterious events surrounding our trio when questions are answered, observations made, loyalties are tested and the elusive William Bell is finally introduced.

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.

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.

Newton, concerned about the consequences of a distressing development involving a high-ranking official, is forced to call to action a sleeping shapeshifter. As Walter and the rest of the team gather evidence, they move the investigation to Massive Dynamic, where Olivia goes on high alert and Walter finds himself in a perilous situation.

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