Walter Bishop opens Pandora's Box. He finds a young Observer once he has hidden in the Pocket Universe.
Astrid awakes during the night with a signal from the radio brought from the pocket universe. She tries to decode the signal but Walter is tripping after dropping a black blotter acid and is incapable to help. The group contacts Anil to help to triangulate the signal and locate the source. Peter and Olivia go to the spot and find skeletons including one with the identity of Sam Weiss and conclude that he died protecting the transmission. Peter finds the location that is broadcasting the signal and he heads with Olivia, Walter and Astrid to an isolated house in an island. Will they find Donald?
- Formerly Harvard University
In the middle of the night, Astrid wakes up to something emitting beeps. She goes to investigate and finds it's the radio they found in the pocket universe. Walter lurks in the darkness. He tells Astrid her hair is beautiful. This is only slightly more weird than the fact that he calls her Astrid.
Peter lies awake in the middle of the night, unable to sleep. His tossing and turning wakes up Olivia. He has had another bad head ache.
Astrid comes to show them the radio. It's on a loop, but it's not Morse code. Olivia tries to consult Walter, but Astrid explains that he's useless: he dropped acid.
He sees a tiny green Tinkerbell flitting around Peter's face and sees a blonde woman over a soundtrack of opera. He's tripping.
He says his old nemesis, the one who was burned in the fire, is haunting him. It's Dr. Warren, the lab assistant whose death put him in the mental institution years ago.
All Walter can say about the message is that the beeps are in A minor. He tells Peter that Nina promised to remove the pieces of brain they put back in after the Observers are defeated.
He's worried about losing them, but Peter doesn't like the plan.
Walter says they're running out of time. Two months ago he was dressed and ready to go outside at 3 a.m., but doesn't know where he was going. Walter's hallucination of Warren says "he" knows where he was going -- the Walter that was.
He figures there must be something left of that Walter that he can use.
Olivia suggests they try tracking the signal. Peter decides to contact Anil for help.
Alone in his darkened office, Walter sees his tiny Tinkerbell bring him a match, which he uses to light a candle. He turns on the TV and sees Anil explaining how a machine will track the signal, a scene that's playing out behind him in the lab.
Warren tells him there's something hidden in the lab.
Anil tries his machine and they get a location.
Zoom in on a location in the woods somewhere, a skeleton hand holds a gun.
Willington, Conn. The team drives into the woods.
On foot, Peter admits he's embarrassed he left Olivia again -- the very thing he promised he wouldn't do. "I'm just so incredibly lucky to have you," he says.
They see an RV nearby and find the skeleton of an Observer. There are two more skeletons, another Observer and a Loyalist. Olivia guesses they were killed 10 or 15 years ago.
Peter looks in the RV and thinks they found Donald -- another skeleton. There's an early prototype Observer gun nearby. He killed the others but died before he could drive away.
Peter follows the location of the signal, and the cable that leads to it, all the way up a tree.
In the RV, Olivia looks through the victim's wallet.
The cable isn't the source of the transmission, it's just a relay being used to bounce the signal from somewhere else.
Olivia tells Peter the body in the van is not Donald. It's Sam Weiss, Olivia's old guide to her powers who "worked" at a bowling alley.
She calls Astrid, but Walter doesn't remember Sam.
Back in the lab, Warren vaguely directs him to find his "secrets." Then he sees Nina. Warren tells him the other Walter would go work with the Observers, if only to show off. But Walter refuses to leave the lab.
He goes to his office, Warren says he's "warmer." He lifts up a panel in the floor. Warren says it's his life's work, "the work that I came to burn the night that I died." HalluciNina tells Walter to put it back.
Green Tinkerbell scolds him, but he flicks her away. He opens the book, it's his old journal.
Cut to Walter in a cab with the book. He flips through his inventions. He asks Warren what "black umbrella" is and why it's in his head. A butler opens the cab door and offers him more acid, which he takes.
He insists to Warren that he's not who she says he is. He realizes he's in Manhattan, outside the Observer precinct. Warren says she's there as a representation of the true him. Walter realizes he has to find his way home.
But then Astrid opens the door and Walter gets out at the shore. They meet Peter and Olivia to rent a boat. They have traced the signal's origin to a nearby island, which looks like Oz to Walter.
As they're heading down the dock to the boat a boat full of Loyalists pulls up and tells them to wait. Peter says they're going to meet his uncle, but when he reaches for his papers, he grabs his gun and shoots the man instead. Olivia takes out a few others and they run for the boat.
They pull away from the dock, leaving the bodies of half a dozen Loyalists behind.
On Thimble Island, Hallicination Warren is still following Walter.
The signal originates from inside a house. Before they can investigate, a middle aged man comes out with a rifle. They say they're looking for Donald, but he says he doesn't know him. He doesn't recognize Walter.
The child Observer comes out, and a woman named Caroline. Olivia explains why they're there. "Richard, we knew this could happen, that one day someone would come for him," Caroline says.
Richard asks what the transmission said. Astrid tries to explain they couldn't crack it, but Richard demands the password.
Suddenly Walter is in an old Monty Python-style cartoon, flying across fields and into a factory with a frog and a seahorse and a Scottie dog. He follows his Tinkerbell to a knight, who turns out to be the other Walter. The frog eats him. He uses a giant key to open a tree trunk and get a black umbrella.
"It's black umbrella," Walter says, out of his dreamland.
Richard lowers his gun. Tinkerbell congratulates Walter.
Inside, Richard explains he and Caroline, his wife, helped the Resistance in the early days. Donald showed up eight months after the invasion and left the boy with them. Donald said he'd worked with a scientist from Boston. They never saw Donald again. They heard he was dead. Before he left, Donald gave them the transmitter to turn on every five days to broadcast.
The boy has lived with them 20 years and hasn't aged a day. He doesn't speak. They call him Michael.
Later, Richard and Caroline say good-bye to Michael and he goes with the Fringe team.
Back at the lab that night, Olivia brings Michael cocoa like she used to make for Etta.
Olivia asks him if he remembers her. He nods, even though he met them in a different timeline.
Walter sees scenes from decades ago, telling Elizabeth he won't give up until he finds a cure for Peter. Warren questions his plan to create a wormhole to another universe. He remembers going through. She says there has to be a line somewhere. Warren quotes Oppenheimer to him to warn him that the portal will destroy both universes.
"Somethings are not ours to tamper with, some things are God's," she says, quoting William Bell from season 4. "There's only one god in this lab and it's not yours," Walter tells her.
Walter breaks his reverie and burns his journal. Warren tells him it doesn't matter, now that he remembers everything he's capable of. HalluciNina tells Walter that with the boy back, they have to keep fighting. "You've been him longer than you've been you," Warren says again.