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.
To penetrate the Observers' headquarters and rescue Michael, their only hope for victory, Olivia must use her abilities and meet with some old friends.
While Walter tries to learn more about the mysterious Donald after Michael's revelation, Windmark undertakes his own quest for knowledge.
The team joins forces with Nina to recover a key piece of the plan that Walter created to defeat the Observers.
The Fringe team is pushed to the brink as they try to save every living person from the schemes of Jones' superior.
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.moreless
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.moreless
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.moreless
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.