At Harvard, Walter cuts another videotape out of the amber and plays it in the lab. It's tape seven and the past Walter is out walking as he describes where the next piece of the plan.
At Etta's apartment, Peter replays the last video message that Etta left. He freezes the image and looks at it for a moment, and then hears someone coming in. Peter grabs a gun and goes to see who it is, and Olivia comes in. She points out that he didn't come home or answer his comm and Peter admits that he turned it off. Olivia sees the frozen video image and Peter says that he wasn't going to stay much longer. Olivia understands why Peter came there, saying that she feels closer to Etta there, and sits down with him and has Peter play the message again.
As they watch, Olivia says that it's fine that he comes there but she just wants him to tell her and that they both understand what the other is going through. Peter apologizes and Olivia notices a bandage on the back of his neck. He lies and says that one of the Observers nicked him during the last gunfight and he's fine.
Walter on the tape goes to 167 Cedar Street and enters the apartment building. He goes to room 413 and a woman complains about the strange noises, and the real Walter writes everything down.
The next morning, Walter goes to the address, unaware that he's been picked up on security cameras. The apartment building has a huge hole torn out of the front. Walter goes upstairs and come across an old woman with a cybernetic eyepiece, the woman from the tape. She warns him that the fourth floor has been red-tagged for twenty years and Walter goes past her and up. He breaks into Room 413 and follows the instructions from the video, taking certain precise steps. Walter reaches a certain point, steps forward... and disappears. Walter finds himself in a clean sterile version of the same building.
Astrid goes to the lab but finds no sign of Walter. Peter and Olivia arrive and Astrid explains that Walter probably left on his own. They play back tape seven and figure that Walter went to retrace his steps. On the tape, Walter boasts that he created an ingenious place, undetectable to Observer instruments, to hide a critical part of the plan. He opened a membrane separating the two universes, creating a pocket universe. Walter starts to give a warning but is distracted by pastries. Walter then warns that the usual laws of physics do not apply within the pocket universe. Astrid confirms that the neighborhood is bombed out and mostly abandoned.
They continue to watch the tape as Walter meets with his friend, Donald, who was waiting for him 21 years ago. He then draws out the lines of dimensional demarcation and indicates the steps to walk. The tape goes blank and Astrid confirms that the tape is undamaged. Olivia wonders why Walter would go alone and Peter admits it's not like his father.
In the pocket universe, Walter walks through the seemingly empty halls of the apartment building. Space is oddly warped in spots as hallways cut off and turn back on themselves. A person appears behind Walter and he hastily ducks around the corner. When he finally looks back, the figure is still there. After a moment, the man walks away and someone behind Walter grabs him. He says that his name is Cecil and asks if Walter know show to get out. Walter says that he does but that he won't say if Cecil keeps threatening him. Cecil releases him and explains that he was in an apartment when the Observers hit the building with light bombs. Walter figures that the explosion blasted Cecil into the pocket universe. Cecil says that he's been there five days and that there is water. Walter asks Cecil to show him but Cecil insists that it's his, and Walter reminds him that he's the resident's only chance of escaping.
Olivia, Peter, and Astrid arrive outside the apartment building.
Cecil leads Walter through the area of reversed gravity to a room where condensation is dripping from the floor onto the ceiling. Walter realizes that there's a refrigeration unit behind the wall but Cecil says that there's nothing back there. Despite that, Walter takes a look for himself and tells Cecil to follow him. He explains that he's been there before but he just can't remember it.
The trio head up the stairs to the fourth floor and call for Walter.
As they walk, Cecil explains that he thought he was in Purgatory. He admits that he was a squatter and stealing things. Walter realizes that there has been a time displacement and tells Cecil that it is now 2036, not 2016 when the Observers attacked the building.
Peter and the others find Walter's footprints in Room 413 and Peter follows the taped instructions. He takes Olivia's hand and they step forward, entering the pocket universe. The rest of the tape now plays normally and the recorded Walter directs them onto the missing piece of the plan.
In Manhattan, Captain Windmark receives a report that Walter has been sighted and prepares to depart.
Peter and Olivia follow Walter's directions into a dead-end that he says isn't. They discover that the corridor bends again and continue on, and on the tape they realize that Walter is talking to not only Donald but another person just off-camera. They catch up to Walter and Cecil and Walter apologizes for leaving on his own. He angrily insists that all he could think of was the next part of the plan. He dismisses Cecil as collateral damage and explains that everything in the pocket universe wraps in on itself, including time. Peter says that there's more on the tape and that it isn't visible unless it's viewed within the anomaly.
Walter plays the tape and his videotaped self explains that they're looking for an apple. He then pulls a small bald child into the camera frame and says that he'll be safe. The real Walter doesn't recognize the child and Peter explains that he was a boy they found during a previous case, living in a demolition site. His empathic abilities helped them solved a case, and Walter realizes that although the case was over 20 years ago, the time anomalies would keep the boy safe and unaged.
They continue playing the tape and find markings on the doors: seahorses, hands, flowers. The Walter-tape version finds a door with an apple symbol and uses the key on the mantle to unlock it. The real Walter does the same and they go inside. There's no sign of the boy. The group watches the tape and see Walter tell the boy to wait for them until they come back to get him. Walter finishes by telling them to see Tape Eight.
As Walter looks around, Peter finds a portable air-degradation unit and they realize the boy was an Observer. Walter says that it doesn't matter and that his plan is now useless. He assumes that Windmark got the information about the boy from his mind and has already taken him. Olivia finds a transistor radio on the nightstand.
As Astrid waits, she sees loyalist troopers and Observers pull up outside. Windmark tells his men to search the entire neighborhood.
Walter storms out and Peter goes after him. He figures that the Observers that would have shut down the portal if they knew about it, so Donald must have come back and moved the boy. Neither one of them know why Donald would do it and Peter suggests that Walter's ally may have believed they were dead. Walter still doesn't remember who Donald is, and Peter figures that they need to find Donald. Olivia calls them back and explains that the radio isn't in the video. It doesn't work but they realize that it will work once they leave the pocket universe, and hopefully lead them to Donald.
An Observer teleports into Room 413 and knocks Astrid out. Another Observer arrives and they both are able to see the otherwise-invisible portal to the pocket universe. They enter it and spot the group. One of them shoots Cecil, killing him. Peter and Olivia lead Walter away through the maze of shifting corridors with the Observers in pursuit. Peter somehow leads them to Room 413 and spots the portal. He throws Walter threw and gives Olivia directions as she catches up. As he passes through, an Observer grabs Olivia. Her gun doesn't work but she throws herself through the portal and shoots the Observer as her gun becomes functional again.
Once they have Astrid, the team heads outside, shooting down the loyalists posted in the streets. Peter tells Olivia to take the others on ahead and then turns as an Observer shoots him down. Peter leaps back to his feet and tries to punch the Observer. At first the Observer has the upper hand thanks to his tech, but Peter fights back and casually catches his punch and then hits him repeatedly. The Observer stares at him and says that knows what Peter has done, and that he's made a grave mistake. Peter teleports behind him and breaks his neck. Peter then picks up his gun and teleports away... as Windmark watches the entire battle.
Olivia, Walter, and Astrid board the monorail and wait for Peter. He arrives just before it departs and Olivia asks how he found the portal. Peter claims that he doesn't know and they take their seats as the monorail departs. Olivia tries to turn on the radio and discovers that the tuning dial is jammed on one frequency. She figures that something will be transmitted.
Peter sits with Walter, who admits that he can't stop thinking about Cecil. He failed to help Cecil escape and didn't even care about him. Peter points out that Walter cared about saving the world, and assures his father that Cecil died 20 years ago when the light bomb went off. Without Walter's pocket, he would have died then. However, Walter isn't consoled, explaining that he considered Cecil an acceptable loss. He wonders if that's who he really is and asks if Peter can see it coming from his mind and heart. Walter says that his actions are those of an arrogant man: his original self before Bell removed the sections of his brain. He warns Peter that he's not safe since the pieces of his brain were reimplanted. Peter tells Walter that he won't let it happen and that his father is their only hope of defeating the Observers. Walter begs Peter not to let him go and Peter promises that he won't. As they talk, Peter looks at Olivia... as his vision alters to what an Observer would see.