You mean for all four seasons so far? OK then, leaving out a few plots so a not to ruin the flow of the summary.
Season 1
[ul]
[li]Olivia gets Peter so that the Fringe division can spring Walter from a mental institution.[/li]
[li]Walter helps them solve mysteries, many, in the first season, caused by experiments that he did.[/li]
[li]David Robert Jones breaks free from a German prison, gathers some equipment, and starts opening up portals to the other side. After finding a suitable location Peter shuts down the portal while Jones is partially inside, cutting Jones in half, killing him.[/li]
Meanwhile a lot of bad things have been happening and attributed to Massive Dynamic and specifically William Bell. Olivia is relentlessly pursuing Bell. Nina grants Olivia a meeting with Bell, so long as it’s in secret. Olivia ends up meeting him in his office in the twin towers on the other side.
[/ul]
Season 2
[ul]
[li]Olivia comes back to this universe in a violent fashion and is taken to a hospital.[/li]
[li]She recovers but remembers her meeting with Bell in fragments.[/li]
[li]A shape shifter kills and replaces Charley. Olivia kills him after a couple of episodes.[/li]
[li]Out of the hospital Olivia gets help recovering from Sam Weiss, who is very mysterious.[/li]
[li]The shape shifters leader’s (Thomas Jerome Newton) head is placed on a new body, reviving him.[/li]
[li]We learn that Walter had three parts of his brain removed, which is why he’s not totally sane.[/li]
[li]It is officially revealed that Peter is from the other side. He gets pissed at Walter for never telling him and blames him for his (alternate) mother’s suiside.[/li]
[li]Newton finds a way to let Walternate come over to our universe where Peter freely goes with him back to the other universe.[/li]
[li]When Olivia was a child, she and other kids were experimented on with Cortexiphan to give them super abilities because Walter and William feared a coming war with the other side. Now as adults some are gathered and go with Olivia and Walter to the other side to retrieve Peter, using Oliva’s power to cross universes.[/li]
[li]On the other side Walternate is studying part of a device and wants Peter’s help. Olivia finally finds him and shows him that the device is a doomsday weapon that Walternate wants to use to destroy our universe.[/li]
[li]Peter goes to leave back to our universe, but Olivia gets replaced by Fauxlivia. Bell has used unstable methods of traveling between universes, his body explodes giving them the energy they need to go home.[/li][/ul]
Season 3
[ul]
[li]Fauxlivia infiltrates the Fringe division and takes over shape shifter operations from Newton.[/li]
[li]Both universes Fringe divisions go to find fragments of the machine in their universe.[/li]
[li]Fauxlivia has sex with Peter and gets pregnant.[/li]
[li]In the other universe Olivia is conditioned to think that she is Fauxlivia. Peter appearing in visions tells her who she really is. She regains her identity and gets alt Bryoles to help get her home. He gets killed because of it.[/li]
[li]Fauxlivia is found out but escapes back to her universe while being taken into custody.[/li]
[li]After the machine is complete Walternate uses blood from Fauxlivia’s baby to activate the machine (because Fauxlivia’s baby has some of Peter’s DNA it can interact with the machine, which was built for Peter).[/li]
[li]The machine in our universe goes wacky. Peter attempts to enter but is knocked out when repelled by a force field. He recovers in a hospital and goes back to the machine. Olivia uses her Cortexiphan given telekinetic ability to open the force field and allow Peter to enter the machine.[/li]
[li]His consciousness is transferred to his body 15 years in the future. There he learns that he destroyed the other side which everybody blamed Walter for and he’s been in prison.[/li]
[li]Destructive worm holes leading to millions of years in the past have been opening up. They are caused by Walternate, the sole survivor from the other side. Very bitter about the loss of his universe he plans to destroy this one.[/li]
[li]Walter realizes that he sent the machine back in time though one of the worm holes. he also figures out that if he can get Peter’s consciousness to travel from 15 years ago until now, he could make a different decision.[/li]
[li]Back in our time, on Liberty island, where the machine is, the alternate Fringe team appears next to our own. Peter gets out of the machine. He tells everybody that he created a bridge to allow everybody from both sides to work on a solution together, instead of sacrificing one side to save the other. He then gets erased from time.[/li][/ul]
Season 4
[ul]
[li]Peter appears to Walter and Olivia as voices and images in their minds. They freak out no knowing who he is. He eventually appears in human form.[/li]
[li]He tries to get Walter to help him go home to his time and his Olivia, but Walter is cold and distant. He tries to get Walternate to help him. Walternate is friendly and willing, but cannot find a way to get Peter home.[/li]
[li]Walter warms up to Peter. Olivia starts getting memories of Olivia from the old timeline that Peter is from. Walter and Lincoln (who has a crush on Olivia) blame Peter.[/li]
[li]We are introduced to a new type of shape shifter which is a danger to both universes. They are revealed to be the product of David Robert Jones, who is still alive in this universe.[/li]
[li]Peter learns from the Observer named September that this is his world and that Olivia is his Olivia.[/li][/ul]