It starts out with some crazy lab experiments a new team is called to investigate. A series of unfortunate events occurs when an Observer realizes he inadvertently alters the future when he distracts Walternate from making the cure, so when Walter crosses over (when Peter was supposed to die), Walter actually saves him and makes him his own. An alternate universe creates a more complex situation where Walternate and Walter actually are part of the Fringe Division, and realize a device must be built to stop the ending of time. It can only be activated by Peter and when he activates he is erased from time and time resets as the two universes are now conjoined and must work together. Walter later realizes that his hubris caused him to do this, a man of ambition, and becomes self-loathing. He is very close to making irrational decisions and actually comes to a point where he is on his knees begging from a sign by God. He admits this to his friend, where his friend tells him it will come into a form as a white tulip. Later on, the love for Peter and emotions for him to leave cause him to come back as an energy, leaking through the timeline and taking physical form once more where no one remembers him except for Olivia. Olivia was dosed with Cortexiphan as a child, a drug used to push the inner limits of the mind, allowing her to have unique kinetic abilities. The Cortexiphan, allows her to remember who Peter is, and Peter must reform his relationship with Walter. As that happens, Walter works alongside another genius named William Bell, who actually turns out to be a traitor and was planning to give this information away all along. He only uses the information to give it to the Observers. William and Walter were both responsible for the dosage of Cortexiphan in Olivia as a child, and William realizes how special Olivia is so they use her as the engine to the collision of the two universes. Because they cannot allow the collision of the two universes, they decide to separate from each other in tearful goodbyes after realizing how similar they were to their parallel selves. However, the severing on the two universes does not stop the course of the universes colliding, and Walter realizes William was using Olivia as an engine to power the magnetization of the two words. In a desperate attempt to save the world, Walter points a gun and shoots Olivia in the head. The rushing of the storms consequently stops, and the universes are now far from each other, and Peter witnesses Olivia's death. Peter is shocked at Walter's crude actions but Walter explains that the Cortexiphan is regenerative and a simple bullet removal allows Olivia to live. Years later, Peter and Olivia have a daughter named Henrietta. She's only 6 when the Observers come to invade the world and split the world into factions known as the Loyalists (Observer siding) and Natives (people who are against them). Etta discovers them 15 years in the future, all frozen in amber and decides to help them. Pushing Walter out with a friend, Walter cannot seem to remember any of the events that happened in the past. Nina Sharp has a piece of the brain Walter asked to have removed, and must be restored in his mind in order for Walter to remember. When Walter remembers, he and the others (Etta) help discover the locations of the other Fringe members. The Fringe members resume their 20 year old plan to defeat all of the Observers. The plan is hidden on separate tapes and builds a design that will destroy the Observers. Every tape is in a different location and each member goes through hell trying to find them. Many sacrifices are made, including Nina Sharp, Henrietta, and Doug, the man who helps Walter -- he turns about to be "September," the Observer who distracted Walternate in the first place. A lot of the Observers dies, with the experiments and weapons collected in the past seasons, back when the team were just an FBI division working on strange cases. Lots of symbolic meaning comes into place such as the six-fingered handprint in blood, the parasites in the water, the super-sized cold virus, skin suffocation techniques, acid gas boiling skin, and especially the butterfly suicide that makes a person imagine they ar ebeing to cut to death, when they are. The key part of the plan is a young boy who seems to be an empath, and he is an anomaly that was not allowed to live as the Observers were writing time. The plan was for the boy to be taken into the future where a doctor would guide the course of natural human evolution from there, creating a paradox where time would reset, the Observers never invaded, and Etta was alive. In a moment of a pure rush of adrenaline the wormhole opens, and Doug originally intends to take the boy into the future, but he is shot before he can run the boy into a wormhole, and Walter makes the bold decision of being erased from time, so time could reset itself. Peter returns to his house, and a letter addressed by a "W. Bishop," comes into the mail. Bewildered by the anonymous sender, Peter opens the letter to find a sketch of a white tulip.
This is such, a beautiful story. I will never forget it.