At Harvard, Walter is alone in the lab and cuts out another Betamax tape from the amber. He plays it and discovers that it's tape seven. His past self is out walking and recording himself, and says that he is going to where the next piece of the plan can be found.
Peter is at Etta's apartment watching a recording that Etta left on her answering machine. He freezes the image when someone comes to the door, draws his gun, and goes to see who it is. Olivia comes in and says that she tried to contact him, and Peter explains that he turned off his comm. She sees the video image and says that she understands why Peter came there, saying that she feels closer to her daughter at Etta's apartment. They sit down and watch the playback again, and Olivia says that it's fine that he comes there but she wants him to share what he's going through so that they can understand each other. Peter apologizes and Olivia brushes the back of her neck, feeling a bandage. Pe3ter claims that one of the Observers nicked him during the fight when they collapsed the wormhole and assures his wife that he's fine.
Walter watches as his past self goes to an apartment building at 167 Cedar Street, Room 413. A woman complains about the strange noises coming from there and the real Walter writes everything down.
The next morning, Walter goes to the apartment building, unaware that he's been identified on the CCTVs. The woman from the tape is there, twenty years older and wearing a cybernetic eyepiece. She tells Walter that that the fourth floor was red-tagged 20 years ago and that it's not safe. Walter goes carefully up the partially demolished steps and breaks into Room 413. He then watches the tape carefully and goes through a series of steps. He then disappears as he reaches a particular spot and finds himself in an alternate version of the building.
Astrid arrives at the lab and discovers that Walter is gone. Peter and Olivia come in and they realize that Walter has left. They check tape seven and figure that Walter went to the apartment. As they watch the tape, Walter's past self says that he created a pocket universe within the apartment building that the Observers couldn't detect. Within the pocket universe, the normal laws of physics don't always apply. Astrid checks the address and confirms that the neighborhood was bombed by the Observers 20 years ago and mostly abandoned.
On the tape, the past Walter talks to h is off-camera friend, Donald, who is waiting for him at the apartment. Walter then draws lines of demarcation on the floor of Room 413 indicating where someone should walk to cross over. As Walter steps into the last position, the tape goes blank even though there's no damage to the tape. Olivia is surprised that Walter went on his own and Peter admits that it's not like him.
In the pocket universe, Walter tries to navigate his way through the apartment hallways, which compress, twist, and double back on each other in defiance of physics. A person appears behind Walter and he ducks around the corner. The person walks away and a man grabs Walter from behind. He introduces himself as Cecil and asks if Walter can lead him out of the apartment. Cecil reluctantly releases Walter and explains that the Observers hit the building with light bombs while he was inside it. Walter believes that the explosion through Cecil through the portal into the pocket universe. He's surprised that Cecil has survived and Cecil says that he's been there five days and he found water. Walter orders Cecil to show him the water and Cecil initially refuses until points out that he's Cecil's only chance of escape.
Peter, Olivia, and Astrid go to the address on the tape.
Cecil leads Walter through an area of reversed gravity to the room where condensation is gathering on the floor and dripping up to a cup that Cecil has placed on the ceiling. Walter speculates that there is a refrigeration unit behind the wall but Cecil says there isn't. After a moment, Walter orders Cecil to follow him, admitting that he's been in the building before but he can't remember it.
The Fringe team duplicate Walter's path into the building and up the stairs to the fourth floor.
As they walk, Cecil tells Walter that he was a squatter and stole things from the other apartment in 2016. Walter brusquely tells Cecil that the year is 2036, not 2016 when Cecil was knocked into the portal. Twenty years have passed outside but only five days for Cecil due to time compression. Cecil is shocked, saying he has a wife waiting for him, but Walter dismisses his concerns and walks off.
Peter, Olivia, and Astrid go to the apartment and see Walter's footprints. They use the tape to follow Walter's steps and Peter and Olivia join hands and step through. The blank part of the tape plays normally within the pocket universe and the past Walter continues giving them directions to the part of his plant hat he hid there.
At Observer headquarters, Captain Windmark receives a report that Walter has been spotted.
Peter and Olivia follow Walter's instructions on the tape as the corridors shift and move around them. They come to a dead-end but Walter on the tape says that it isn't. Olivia realizes that there's a corner that blends into the adjoining wall and they continue. As they walk, Peter realizes that Walter is talking not just to Donald, who is holding the camera, but another person off-camera and lower. They find Walter and Cecil and Cecil and Walter apologizes for going off on his own. He then loses his temper, saying that he became obsessed with finding the next part of the plan. Walter dismisses Cecil as "collateral damage" and explains that time and space are compressing around them. Peter tells his father about the restored section of the tape and how it only plays the rest of the directions within the pocket universe. They continue watching the tape and past Walter explains that they're looking for an apple. He then pulls a bald boy into view of the camera and they realize that it's the child empath they encountered in the first year of the Fringe division. Walter realizes that although the case was over 20 years ago to them, the anomalies in the pocket universe mean that the boy has only aged a matter of days.
As the group follows the taped instructions, they discover that the doors are marked with various symbols: flowers, hands, seahorses, leafs. Past Walter leads them to a door and reveals the key is hidden above the sill, and the group uses the key to go inside. There's no sign of the boy inside and they watch on the tape as Past Walter tells the boy that only a short time will pass and that he's to wait until they come to get him. He then leaves a message on the tape saying that they should see tape eight for the next part of the plan.
Peter searches the room and discovers that there is a portable air-degradation inside. They realize that the boy is an Observer, but Walter flies into a rage and says that it doesn't matter because his plan is useless without the boy. He figures that Windmark somehow pulled the information out of his mind and already came and took the boy. While Walter storms out, Olivia finds a transistor radio on the nightstand.
As Astrid waits in Room 413, she sees the Observers and a squad of loyalist troopers pull up outside. Windmark gets out and tells his men to search the entire neighborhood.
Peter goes after Walter and points out that the Observers would have shut down the portal if they gained the information from Walter's mind. He suggests that Donald may have come back and moved the boy, even though they don't know why he would have done so. Peter suggests that Walter's ally may have assumed they were dead after they disappeared years ago. Olivia calls them back in and shows them the radio, pointing out that it isn't on the nightstand in the video so someone, probably Donald, left it there for them to find.
An Observer finds Astrid, teleports in, and knocks her out before she can fight back. Another Observer arrives and the two of them are both able to see the portal. They enter it and track down the group, then open fire on Cecil. The squatter is killed instantly and Peter and Olivia lead Walter away. Peter manages to navigate the maze and takes them back to Room 413. He spots the portal and shoves Walter through, and then points out the portal location to Olivia before stepping through herself. As she goes to the portal, an Observer teleports in and grabs her. Her gun doesn't work but she throws herself through the portal, pulling the Observer with her. Olivia's gun works in the real world and she kills the Observer with it.
The trio gets Astrid and heads outside, shooting down the loyalist standing guard. Peter sends Olivia and the others ahead while he covers their escape. As they round the corner, an Observer teleports in and shoots Peter down. He recovers and attacks the Observer, who easily deflects his blows... at first. Peter soon matches the Observer's strength and agility thanks to the implanted tech, beating him down. The Observer realizes what Peter has done and tells him that he's made a grave mistake. Peter teleports in behind him and breaks his neck, and then teleports away... unaware that Windmark has watched the entire encounter.
Peter catches up to the others on the monorail just as it departs. Olivia asks how he guided them out of the pocket universe. and Peter claims that he doesn't know. He sits up front with Walter while Olivia sits with Astrid and examines the radio. They realize that the tuning dial is jammed on one specific frequency and figure that someone will transmit directions to them.
Walter tells Peter that he can't help thinking about Cecil and yet he doesn't care about him dying. Peter points out that Walter is trying to save everyone and points out that Cecil technically died 20 years ago, and it was only Walter's pocket universe that let him continue living for a few more days, relative time. However, Walter tells his son that he considered Cecil an acceptable loss. He warns that he's not safe and that his old self is coming back now that the pieces of his brain have been reimplanted. Peter assures him that he won't let him go back to the way he originally was, and that Walter is their only hope of defeating the Observers. He promises that he won't let Walter revert. As Peter looks at Olivia and she smiles back, he realizes that he's seeing things in the same vision as the Observers.