Walternate asks Olivia if he can begin a series of experiments on her, with the hopes of her learning how to cross between universes.
A man frees his twin brother trapped in amber in a quarantined area. The Fringe Division is called in to investigate and figure out that someone is now missing.
Walternate developed amber to help his universe stop disintegrating. The victims enclosed in the amber are alive, but removing them would weaken the structure.
The Fringe Division identifies the missing man as Joshua Rose, bank robber.
Olivia and Agent Lee then search Rose's apartment and narrowly escape before the building explodes. They next question Matthew Rose, Joshua’s twin brother. They want to see if Joshua has attempted to make contact.
It turns out Matthew, the good twin, was the one trapped in amber. Joshua has been trying to free Matthew because it was his fault his brother became trapped in the first place.
Walternate puts Olivia in a sensory deprivation tank, to free her of distractions so the part of her brain that allows her to travel between universes is more assessable. With the help of a drug Olivia is able to cross over.
Olivia's mom goes to Agent Broyles and expresses concern that her daughter went back to work too soon, and that she hasn't been herself lately. Broyles then takes Olivia off the case.
Olivia learns Joshua's next bank robbing target. The Fringe Division moves in. It is a class two breach and Broyles wants to quarantine the area with amber to stabilize the molecular structure.
Joshua really set the bank robbery up, to sacrifice himself and let his brother live a normal life. Joshua is the only casualty of the quarantine.
Olivia figures out the truth about the twins but decides to drop the investigation and leave Matthew alone.
Olivia has a vision of Peter which prompts her to want to get back into the deprivation tank. She crosses over and learns the Twin Towers have fallen, just like Peter told her. She also places a call to her niece.
Olivia then tells Walternate that she wasn’t able to cross universes.