On the Other Side at Liberty Island. Dr. Anderson talks to Olivia Dunham and tries to convince her that she's suffering from stress caused by a head injury, and that she is suffering from delusions that she's from a parallel world. Olivia insists that her mother isn't alive, and she doesn't work with Fringe agents Lincoln Lee and Charlie Frances. Dr. Anderson shows Olivia a picture of her winning an Olympic award in marksmanship, but Olivia doesn't believe it. Olivia concedes that the idea of parallel worlds sound insane when she first heard it, but she's had to accept it. Next, Dr. Anderson asks her about Peter, and Olivia explains that she's a civilian consultant for Fringe Division. She admits that Peter had to leave with Walter to return to his other dimension.
In his office, Secretary Walter Bishop watches the exchange and tells Agent Brandon that the memory transfer process isn't working, and they need to give Olivia another dose. Brandon warns that it could kill her, but Secretary Bishop warns him that they are at war with creatures from a parallel dimension, and Olivia holds the secret to travel between universes. If they can recruit her, they can understand how her ability works... and use it to end the wary.
A soldier takes Olivia to a chamber for treatment. On the way, she memorizes the security code for the elevator. In the treatment room, two scientists give Olivia injections involving blood from her counterpart, "Bolivia." Olivia fakes asphyxiation and when they unstrap her to give medical assistance, she stabs one with a hypodermic and knocks the other one out. She then runs out of the room, knocks out her escort, and takes her gun. As Olivia enters the elevator, two guards spot her and open fire as the alarms go off. She gets to the surface and flees through the woods to the water separating Liberty Island from New York City. With the soldiers closing in, Olivia has no choice but to dive into the water.
The next day in Manhatan, a taxi driver, Henry Arliss Higgins, is surprised when Olivia gets into his cab and forces him to drive by threatening him with the gun.
On Liberty Island, Colonel Broyles of Fringe Division tells Secretary Bishop that the Harbor Patrol believes that Olivia drowned trying to swim against the currents to the opposite shore. Broyles doesn't believe it and Secretary Bishop tells him to find Olivia.
As he drives, Henry figures that Olivia is some kind of patient. She explains that the government has been performing experiments on her to make her think that she's someone else. Olivia spots a photograph of Henry's wife, Jasmine, on the dashboard and asks to see his Show Me ID. She then has him pull over to a clothing store and orders him to go in and get her something to wear. When he wonders why he should, Olivia warns him that she now knows where his family lives.
Lincoln Lee, Olivia's partner, is still burned after his encounter with the pyrokinetic in Central Park and undergoing physical rehabilitation at the Department of Defense hospital when Charlie Francis, his teammate, comes in. Unaware of what has really happened, Charlie tells Lincoln that he has been told that "their" Olivia suffered a head injury during the showdown at the opera house and is suffering from a psychotic break, while the alternate Olivia returned to her reality. Colonel Broyles arrives and tells them that Olivia has escaped from the treatment center on Liberty Island.
Henry returns to his cab with Olivia's clothing. As she dresses, he notices a tattoo of a sun on her neck and comments on it. She tells him that she doesn't have a tattoo, and that the authorities gave it to her to make her think she's her counterpart, Bolivia. Henry tries to patronize her and Olivia warns him not to, and insists that she's telling the truth, and then tells him to drive to the opera house so she can go home.
Broyles explains that they don't know where Olivia is going, but they need Charlie to help them search. Lincoln insists on going and informs them he has six hours before he has to return to the hyperbaric chamber for more nanite treatment.
Olivia arrives at the opera house where people are protesting against the government. She tells Henry to stay and repeats her threat against his family. As she approaches the opera house, a policeman recognizes her as Bolivia, but warns her away when she tries to go inside. He pulls her away just as the authorities release a cloud of amber throughout the building to quarantine. The amber hardens, making it impossible to enter.
Broyles, Charlie, and Lincoln go to Fringe Headquarters and check in with Agent Farnsworth. She calculates that Olivia is likely to either go back to the opera house, try and leave the country, or make contact with people she thinks she knows. When they get a report that Olivia was seen leaving the opera house in a taxi, Broyles starts tracking taxis.
As he drives, Henry gets a call from his wife, Jasmine. After he finishes, he asks Olivia if she has someone. She admits that Peter is the person in her life, and he helped her get there. Olivia gets an idea and tells Henry to drive to the address of Massive Dynamic. He has never heard of it, and says they have to stop for gas. While he refills the cab, Olivia goes into the restroom and checks the tattoo on her neck. She then goes into a stall and cries briefly, and then comes out. She finds Lincoln waiting for her. Lincoln asks her to surrender so they can get her treatment, but Olivia insists she's not who thinks she is and draws her gun. Lincoln reluctantly turns over his sidearm and Olivia locks him in the restroom. As she heads for the cab, more Fringe agents pull up. Olivia fires to force them to keep their distance and gets in the cab. Charlie comes out and Olivia pulls off an amazing shot, hitting the valve on the propane tank behind him as Henry drives. The tank explodes, stunning Charlie and giving Henry and Olivia time to escape. As they drive, Henry realizes that Olivia is telling the truth and removes the hidden tracking unit.
Colonel Broyles tells Secretary Bishop what has happened. The Secretary is satisfied with what happened, and shows Broyles footage of Olivia shooting the valve. They realize that only one person has that kind of accuracy, and Secretary Bishop figures that the memory treatment they gave to Olivia is starting to work.
Henry arrives at the address that Olivia gave him for Massive Dynamic. There's nothing there but a park, and Olivia realizes that Massive Dynamic never existed on the Other Side. Henry asks her if she's okay and she suddenly remembers an address in Tarrytown, New York. She tells Henry to take her there. As they drive, Henry notes that Peter must be very important to her, and Olivia thinks he's talking about Frank Stanton, Bolivia's fiancée.
Charlie goes to see Frank and asks him if there's anything they might have missed that would give a clue to Olivia's location. Frank says that Marilyn is back in town.
Henry drives Olivia to a house in Tarrytown and volunteers to wait for her. She tells him to go home to his family, and insists that she's not crazy. Henry explains that several years ago, he had problems realizing his true self, and only Jasmine believed in the man he really was. He tells Olivia that sometimes you have to have faith in the unseen. Olivia thanks him for his support and goes to the house. When no one answers, Olivia goes around the back and enters through a window. She hears music and goes into the living room to investigate. There's a dog, and a mantle with photos of herself and her dead mother. The Marilyn Dunham of the Other Side comes in, sees Olivia, and assumes that she's her daughter. Olivia insists that she isn't, and Marilyn wonders how she knew about the address, and Olivia starts to waver. When Marilyn talks about Olivia helped her pick out paints for her work, Olivia starts to remember Bolivia's childhood, and runs into Marilyn's embrace, sobbing.
A little later, Charlie arrives and Marilyn ushers him in and shows him that Olivia is there. She greets him happily.
Secretary Bishop tells Agent Brandon that his plan was successful after all. Brandon explains that the adrenalin created by Olivia's escape caused the lymphocytes from Bolivia that they injected into Olivia to do their job.
Henry watches as Olivia leaves with Charlie, and then drives away.
Secretary Bishop tells Colonel Broyles to give Olivia the weekend off and then put her back on the Fringe team. He objects, insisting that she represents a danger, and asks why they should take the risk. Secretary Bishop simply repeats his order and signs off.
On Olivia's Earth, Peter is meeting with Senator Dennis Van Horn and describing what happened to him on the Other Side. Van Horn wonders why Peter came back rather than stay there and sabotage Secretary Bishop's work, and Peter refuses to answer.
Outside, Bolivia is waiting with Walter, who is busy eating Oreos. Peter comes out and suggests they go to dinner. He admits to Bolivia that he couldn't stop thinking about her, and gives her a kiss as they go.