The acclaimed series that has explored the human condition through the prism of parallel universes, unexplainable phenomena and unimaginable threats, reaches a milestone 100th episode and comes to an epic and climatic conclusion. Peter, Olivia, Walter, Astrid and Broyles face off against the Observers in one final and extraordinary battle for the fate of mankind. The five-season saga comes to an epic and emotional end.
September, talking to December, implores him to help fix a key component of the device, an initiating reactor, to send Michael to the future, despite knowing this will erase September from time. September pleads to the same compassion that December, like the others of the original Observer team, developed for the humans. Later, September regroups with Fringe to explain the failing reactor, and describe the function of the device: to create a wormhole using the two Observer cylinders ("Five-Twenty-Ten") as stabilization points on either end, and the large electromagnet ("The Human Kind") needed to launch the second cylinder into the future of 2167. Once the wormhole is stabilized by the red rocks from the mine ("The Recordist"), Michael would
be sent through, to meet an agent to take him to the Norwegian scientist as to stop the experiment that would be responsible for creating the Observers. As they discuss this, Olivia is still concerned while Michael willingly let himself be Walter
captured previously ("The Boy Must Live") and believes him to have expected to be rescued. One additional part is necessary to assure the magnet's operation, a synchroscope, and Peter begins to dig through the amber in the lab to look for it.
Captain Windmark, having discovered Broyles' alliance with the Fringe team, interrogates him about the recovery of Michael from a secured facility, believing him to be "The Dove", a mole for the underground ("The Bullet That Saved the World"). Olivia and Peter waiting inside the Car
Windmark leaves, and Broyles sets off to meet Fringe until he realizes that Windmark intended to follow him to the Fringe team, and keeps them distracted. Though he tries to elude them, Broyles ends up captured.
Walter and Astrid
In looking through the amber, Peter finds a tape that is addressed to him in Walter's handwriting. The tape is a goodbye message from Walter to Peter recorded before they were frozen in amber, and alludes to an envelope that he will receive at some point; Walter in the present explains that he will be the one to travel with Michael into the future, having already inoculated himself in 2015 to do so, and will be forced to live out their
lives there as to ensure that a paradox is not created and that the Observers are wiped out from the point of the original invasion, in 2015. Walter and Peter share an emotional moment, Walter calling the time they have had "stolen" but appreciated every minute of it, and calls Peter his "very favorite thing".
Olivia and Peter wearing mask
Olivia and Astrid go to get a new initiating reactor from December, but find him hanged and the reactor stolen by other Observer and Loyalist forces. September asserts that there's no technology in 2036 to create the reaction needed. Olivia looks to Michael to gain insight; he motions her to be quiet, during which Astrid comes up with the idea of using one of the Observer shipping lanes as their wormhole ("An Origin Story").Olivia kills Windmark.
They begin to make plans to take over one of these the next day, when they learn of Broyles' capture from Anil. They set to use many of the past Fringe biological materials to kill many of the Observers and Loyalist forces. They obtain the control cube needed to operate the shipping lane and rescue Broyles along the way. Meanwhile, September reveals to Walter that he has taken the only spare dose of inoculation to take Michael into the future instead of Walter, having come to have feelings for Michael.
The Fringe team races ahead of the Observers to hijack the wormhole and launch one of the Observer Beacons through it. As they get ready for Michael, Windmark arrives and attempts to grab Walter and Micheal
him. September, Peter, and Olivia fight Windmark. Windmark gains the upper hand, but Olivia, under emotional duress of fighting for her daughter Etta, has her latent Cortexiphan powers trigger that draws power from the surrounding city ("Ability"), and psychokinetically smashes Windmark between two cars. Windmark is smashed between two cars.
September races to take Michael to the wormhole but is shot and killed by a stray bullet. Walter realizes his fate, and decides to take Michael through the wormhole as Peter, Olivia, and Astrid look on. Before entering the wormhole, Peter says goodbye to Walter.
Peter, Olivia, and their young daughter Etta are enjoying a day in the park (as seen in "Transilience Thought Unifier Model-11" and throughout the season). The Observer invasion does not occur, and the family returns home. When Peter checks the mail, he finds an envelope addressed to him from W. Bishop, containing only a piece of paper with a drawn white tulip on it. ("White Tulip")
• "Walter, twenty years ago when I agreed to let you be the one to take him, I didn't have the feelings I have now. Later, when I began to realize the height of his intellect and what you call the depths of his emotion, still, I couldn't understand what it was that I meant to him. And I was unable to reciprocate. When I saw you. When I saw Peter, and saw what he meant to you... then I understood what my feelings were. And why they were important." - September (to Walter, on what his son Michael has grown to mean to him over two decades as his own emotional capacity has developed after reverting from Observer technology)
• "Peter, I sent you a letter. It contains something of mine.... I imagine you called me to ask why would you send such a strange letter? And when you tried to call, I didn't answer. So you came to find me at the lab. But I was not to be found. I was here one moment and vanished from the face of the Earth the next. I want you to know, I'm fine. And living many, many years from now. You will never see me again. You will never again because it had to be this way to ensure the future of our humanity. Your future, the future of Olivia and the future of Etta. I don't want you to be sad. The time we had together, we stole. I cheated fate to be with you, and we shouldn't have had that time together, but we did. And I wouldn't change it for the world. I don't want to say goodbye, but I will say, I love you, son." - Walter (on videotape from 2015 to Peter in 2036, foreshadowing his unexplained disappearance at the instance an invading force from 2609 AD was supposed to arrive, if they had existed, and Walter's one sign that God exists, a simple sketch of a White Tulip in the mail)
• "I know in my soul this is what I am supposed to do. I want you to give Olivia your daughter back. I want to give you your life back. As a father, how could I not do that for you? What I said on the tape about stealing time with you, I meant it. I wouldn't trade it for the world. …You are my favorite thing, Peter. My very favorite thing."
• "Destiny can be changed. But you have to have the will to change it... even if it requires sacrifice." - September (to December)