When several cars stop working at a road to Vermont, followed by a plane crash, Olivia, Peter and Walter are assigned to investigate. On the return, Walter asks to stop at a diner to eat pie and they are attacked by the attendant that is killed by Olivia. They find most of the population dead and a wounded survivor called Cliff that explain that most people went crazy a couple of days ago. They meet a group of survivors and Walter concludes that people from both universes are merging in their doubles and they are trapped in the town. Only those that do not have double in Westfield have survived. But the greatest problem is that the town will be completely destroyed and only the center of the merged town will be a safe place.
Peter, Olivia and Walter come face to face with a mysterious and terrifying Fringe event as they get trapped in a town that there's no escaping.
- Peter and Olivia make love in bed. She asks him to tell her he loves her, he does.
Olivia wakes up alone in her bed to her phone ringing. It's Peter. He and Walter might have had a breakthrough, but he needs her help.
At the lab, Walter is concocting a morning cocktail of cinanamon schnapps and butter. They finished a biomechanical interface for Peter to use on the machine, just like he had in his timeline. They need Olivia to ask Broyles's permission to try it on the machine.
A trucker drives down a road in the woods and slowly his truck sputters to a stop. He gets out and sees objects in his car hovering off the floor. Other people are stopped too. The group stands there as a plane flies low, they realize it's flying too low and tilting to the side. It zooms over them and crashes. All their cars turn back on.
Broyles, Olivia and Astrid hit the scene, there are no survivors of the plane crash. Astrid can't reach Walter on her earpiece. He and Peter stroll up behind her. Olivia's impressed Walter left the lab.
Walter kicks off a car's rim and flings it against another car. It's magnetized.
After collecting samples, Olivia, Peter and Walter stop in Westfield, a small town, so Walter can get some pie at a diner. The man behind the bar chats with him as he serves him pie and coffee. Walter learns they're in Vermont. Peter goes to the bathroom.
Olivia's cell phone isn't working so she goes to find a payphone to call Broyles. She finds an empty car with its engine running. The phone doesn't work.
Peter hears something coming back from the bathroom. The man behind the counter asks Walter what he wants to order, when Walter reminds him that he already ordered, the man turns nasty. Then, in a second he remembers to get Walter his pie.
Peter opens a door in back and finds two people wounded on the floor.
Walter notices the man behind the counter has double irises. There's a body on the floor behind the counter. The man lunges at Walter with a knife and he tries to fend him off while calling for Peter.
Peter rushes up and grapples with him for a moment until a shot rings out. Olivia shot him. Walter checks the man's eyes.
Olivia says the whole town is deserted and she has no cell reception. The wounded man in back is in bad shape, they have to take him to the hospital 20 minutes away.
In the car, the wounded man mutters that he can't leave. Olivia passes the "Welcome to Westfield" sign. Then she passes it again. Wounded Cliff says again they can't leave.
They return to the Westfield Sheriff's office. Walter scrambles to give Cliff a blood transfusion. He's seen this phenomenon before... in "Brigadoon," a musical about quaint town that no one could leave.
Cliff tells them everyone's gone crazy. It started three nights ago. His sister called and said there was an intruder. He went over and found his sister's husband shot dead -- by her. They'd been married 18 years, but she didn't recognize him.
It was like she had someone else's memories. Walter thinks it sounds like schizophrenia, but the whole town has it. Cliff explains that people would get confused, then have tremors and sometimes turn violent. He and his wife and daughter are immune and hiding out in the high school. He went to the diner to get them food.
Peter wants to try to contact Broyles with a radio. They arm up. Olivia mentions there's an army base 50 miles away and remembers a case they had where an army experiment caused people to get disfigured. Walter has no idea what she's talking about, but Peter says he had a case like that with his Walter and his Olivia.
Walter asks for a weapon, Peter gives him pepper spray. Olivia gives Cliff a gun.
Outside, there's a man in the street moaning as he walks. He's covered in blood. He walks by. Olivia's car won't start, which Walter attributes to the electromagnetism.
As they're walking, Olivia's arm won't stop shaking. She gets dizzy and has trouble speaking. She says it felt like someone else was in her head for a minute. She turns her gun over to Peter, worried that she has whatever the town has.
At the school, a man named Brian lets them in. There are 12 people there, one went crazy this morning. Walter asks to examine her.
Theresa opens her mouth and shows two rows of teeth. Walter draws her blood. Theresa expects her husband Lee home any moment. She's talking about him, then remembers he's dead. Then she loops back to expecting him home.
Peter comes back, reporting he couldn't get a radio signal. He urges Olivia to tell Walter what she's experiencing. He draws her blood and assures her she's probably fine.
Olivia tells Peter that Walter has seemed better since he's been there. Olivia asks about the other Olivia. Peter says she gave him a place to call home, they even had a regular Friday routine of getting take out from the same place and watching movies.
They hear a scream and find Theresa dead in the bathroom with her wrists slit. She has double irises. Cliff regrets that he didn't take a job in Philadelphia when it was offered last year and get out of Westfield.
Walter pages Peter and Olivia. He found twice the genetic material in Theresa's blood than she's supposed to have. It reminds him of an experiment he and Bell did once, combining a small part of the two universes. It hurt their fish test subjects and caused magnetic problems. He thinks the universes are overlapped in the town and people are merging with their dopplegangers, which is why they have divergent memories. He doesn't think it's reversible. But Olivia's blood was fine.
He thinks the people who aren't affected are fine because their dopplegangers aren't in the town in the other universe. So other Cliff did take that job in Philly and that's why this Cliff is OK, because he's the only one in town.
Walter can't imagine an energy source that would merge an entire town. Peter wonders if David Robert Jones is involved.
Walter says there's more coming. The ground shakes. Cliff comes to take them onto the roof. There's an energy field on the horizon slowly sucking structures into oblivion.
The two merged towns are creating excess matter. Walter thinks both towns will be destroyed and them along with them. He thinks there's nothing they can do. Olivia suggests Peter talk to him.
Peter suggests they could be safe if they find the center of the merger, like the eye of a storm. Olivia asks Cliff and Brian to find older cars without electronics to transport everyone. Walter and Peter do some calculations on a map and find the center. Brian pulls up in a school bus.
They all get on but a man in the back starts attacking Peter. The man has two faces on his face. Peter struggles with him and Olivia doesn't have a clear shot from the front of the bus. Walter intervenes with his pepper spray and they kick the man off.
The bus reaches the safe spot. They run for it as objects disappear behind them. They hunker down in a bike shop and as Walter is assuring everyone they're safe, the front window blows out. They take cover in the back as things disappear behind them.
Some time passes and the noise has stopped. They look outside and see nothing around them. All the features of the land are gone and it's stripped bare. Only a few buildings remain.
Broyles and rescue squads are on the scene. The whole town was wiped out -- 500 people. They found devices placed around the perimeter with traces of amphilicite. David Robert Jones. He only used a fraction of the amphilicite he had.
Olivia tells Cliff the FBI will relocate his family. He's just glad they have each other.
Back at the lab, Peter is ready to head out but Walter is making crepes. Walter looks forward to seeing him in the morning. Peter wants to get started again on the machine, which reminds Walter that he's leaving.
Peter drops by Olivia's. She goes to pour him a drink. She's ordered their usual Friday take out - his routine with his Olivia. She kisses him hello. Peter tries to figure out what in the world is going on with this Olivia.