The dying Observer comes to see Walter and Peter, who must take extreme measures to learn what secrets he hides and determine if he knows where Olivia is. Meanwhile, David Robert Jones tries to force Olivia to use her cortexiphan abilities by torturing Nina.
Olivia, Peter, and Walter visit the town of Westfield to investigate a report of Fringe activity, and discover that they are trapped.
While trying to cope with a new set of memories, Olivia discovers that a mentally ill patient who is a suspect in a string of murders may be connected to her own past. Meanwhile, Walter travels to the Other Side to discover the cause of Olivia's problems.
The fate of humanity is on the line as Walter plans to make the ultimate sacrifice to stop the Observers before they were ever created.
The Fringe Division of the Other Side must deal with both a visit from Peter and a new enemy, who is preparing a worlds-spanning operation to gain the mineral he needs to provide energy for his master plan.
The Fringe team visits a widow who is connected to a mysterious event. Meanwhile, Peter and Olivia try to resolve the issues between them.
The Fringe team on both sides fight a common cause and developments are made regarding the Cortexiphan children.
While David Robert Jones goes after his next target, Walter visits the Other Side to help the team's counterparts with an investigation into a Fringe case that touches on both worlds.
In the year 2036, a new Fringe team takes on the Observers in a war that will change everything. But to win, they must resurrect a legendary figure from their past, someone who holds the secret to defeating the Observers once and for all.
While Olivia and Lincoln try to return Peter home, they try to cope with the looming threat of the transparent shapeshifters. Meanwhile, a traitor is revealed and an old enemy emerges from the shadows.
Lincoln teams up with the Other Side and together they investigate a vigilante with a connection to the shapeshifters.
After infiltrating a subway station to recover a vital piece of Walter's plan, the Fringe team meet up with an old friend... and must determine if he can be trusted.
While Peter and a local sheriff investigate murders tied to Newton, Walter is worried that he'll be sent back to St. Claire's, and someone new arrives from the other Earth.
An electrical engineer and his wife, a professor of theoretical physics, are involved in a series of time loop anomalies.
A suicide incident occurs at Grand Central Station, and Olivia dreams about it. Meanwhile, shocking details emerge about the ZFT manuscript and Olivia's past.
To penetrate the Observers' headquarters and rescue Michael, their only hope for victory, Olivia must use her abilities and meet with some old friends.
Olivia returns from the alternate reality and Peter tries to get information about her visit. Walter makes some custard for his son's birthday, while Broyles deals with the threat of a government shutdown of the Fringe Division.
While Peter and Olivia investigate murders involving an inexplicable toxin, Astrid and her Other Side counterpart meet for the first time.
Peter takes extreme measures when the team learns of a way to stop the Observers from changing Earth's atmosphere and wiping out humanity.
The Fringe team is pushed to the brink as they try to save every living person from the schemes of Jones' superior.
While Walter tries to learn more about the mysterious Donald after Michael's revelation, Windmark undertakes his own quest for knowledge.
The translucent shapeshifters return to plague Fringe division, and a former Massive Dynamic scientist is involved. Meanwhile, Walter meets with Nina Sharp.
In the year 2036, Peter, Astrid, Walter, and Etta set out to find Olivia and free her from amber. Once they do, they discover she holds the key to finding the plans for a weapon to defeat the Observers... but Walter is captured and interrogated for the same information.
Walter is forced to relive his past while investigating a series of spontaneous human combustions, while David Robert Jones begins his end game.
Bolivia and her team call upon their counterparts from This Side for help when a serial killer goes on a bloody rampage. They recruit the killer's This Side counterpart, a professor of forensic psychology, and try to transfer him to the Other Side without his knowledge to put together a profile on his other self. However, things soon go out of control when the professor realizes what's going on.moreless
Walter is forced to leave the lab for the first time in years when he and Olivia go to Massive Dynamic to examine files that may connect one of Walter's Cortexiphan test subjects to a new series of crimes.
As Walter tries to deal with his hallucinations, the Fringe team takes on a case of two 12-year-olds who died under mysterious circumstances after bullying another boy... and their bodies decompose at a remarkable rate of speed.
The team joins forces with Nina to recover a key piece of the plan that Walter created to defeat the Observers.
While the Fringe team tracks down a girl who can predict the future, Olivia tries to cope with the message given to her by the Observers.
Peter reaps the consequences of spying on an Observer leader. Meanwhile Olivia's search for another tape leads her to a woman who seems to be able to divine the future.
The fight against the Observers intensifies and a Fringe team member plans an attack on his own.
While Peter and Olivia deal with the emotional consequences of the Observer's revelations to Peter about his future, the Fringe team investigates the case of a killer who seems intent on murdering... love.
The team investigates a case involving a bizarre mutation that Peter solved in his original timeline four years ago.
The Fringe team investigates a pocket reality occupying an apartment building, and Peter learns that he has the power to stop the Observers.
After Walter's mind is damaged by Windmark's telepathic probe, the team goes to Walter's old Harvard lab to find the information they need to defeat the Observers.
The teams on the two worlds work together to solve the case of a shapeshifter, and Agent Lincoln Lee joins his world's team when no one remembers the existence of Peter Bishop.
While Olivia copes with migraines, she and her team investigate an invisible force which kills its victims and causes the body to turn a ghostly white. As they trace the pattern of deaths, the Fringe team realizes that the force is linked to someone who died of an unknown genetic disorder.moreless
Olivia, Walter, and Peter are brought in to try and stop a killer with the ability to liquefy the human brain.
While Olivia and a recently-recovered Peter investigate a mysterious signal coming from a forest, Walter uses LSD to try and recall his memories of his plan to defeat the Observers.
The Fringe team meets with a group of humans who have taken refuge in the forest and seek to preserve humanity's history any way they can.