In Park Slope, Brooklyn, a couple entertain friends at their seventh-floor apartment in the Rosencrantz building. Outside, an older woman tells the doorman that she won't spend another minute in this building. As he helps her into a cab, bodies suddenly rain onto the sidewalk from the couple's balcony.
The next morning, Walter whips up blueberry pancakes and tells a dismayed Peter that he's invited Olivia for breakfast. After she arrives, Walter puts "Feelings" on the turntable and splits. Awkward. She and Peter again discuss his feelings for Bolivia. He admits that he still thinks about "her" - because he spent so long imagining what being with Olivia would be like. And it was beautiful. Olivia says that she took that away from us, not me. And now, he asks, who's the one stopping us? Then Broyles calls.
In Brooklyn, Broyles reports six party guests fell to their deaths, but the balcony has no structural damage. Above them, an old lady looks out her window and closes the curtain. Ever weirder, Peter and Walter discover, it's like the people went straight through the balcony to the ground. Olivia reports that, thanks to such incidents as new water pipes exploding and mysterious electrical surges, residents think that the building is haunted.
Walter flips a coin ten times, getting heads each time. The laws of physics are being disrupted here. One second the balcony's there, the next it's gone. As in the other universe, this world is starting to come apart at the seams. Back at Harvard, an agitated Walter turns arrogant and impatient. He has Peter and Olivia take equipment to the building so he can track irregularities, and he asks Astrid for the case file from that chemical attack on the commuter bus a few years ago.
Olivia and Peter set up a seismograph, but the readings are normal. They head to a nearby bar just as the lady from the window, Mrs. Alice Merchant, returns home. Olivia reminds Peter that he said being with her was beautiful. She wants to know what that feels like. She kisses him, then excuses herself. He follows her, and she explains he glimmered when they kissed. That's how she sees things from the Other Side when in a heightened emotional state. She's afraid she's incapable of being vulnerable. She looks at the building . . . and sees a glimmer outside Mrs. Merchant's window.
Inside, Alice looks at a photo album. The room is glowing. At Harvard, the equipment registers an event. Peter and Olivia crash into Mrs. Merchant's apartment, 6B, as the lights flicker madly. Olivia sees what she's gazing at: a ghostly image of the woman's dead husband.
Alice and Derek were married for 45 years. They never had children. Alice explains that he died a couple months ago, when the fuse box blew. They flipped a coin, like usual when there was a chore neither wanted to do, and Derek lost. A short in the wiring killed him instantly. A few days after the funeral, she was really pining for him . . . and he came to her.
Walter says that the building isn't haunted. He thinks Derek's double has the same apartment on the Other Side. Alice is somehow seeing him and mistaking him for her husband. That's why Olivia sees him too. And this is not good. Every incident weakens the soft spot, until eventually it becomes a vortex, a hole sucking in everything around it. Like what happens on the Other Side. That's why Walter wanted the file on the bus attack (where they first encountered amber). He tells a stunned Olivia and Peter that they should respond to a vortex here just as they do Over There: With quarantine.
As a Massive Dynamic team works on reproducing amber, Peter and Olivia brainstorm an alternative. Privately, Walter confides to Nina that he had believed Walternate was evil and would use any means necessary to get what he needed. But now he's arguing that they should do exactly what Walternate did.
Peter theorizes that Other Derek's wife lost the coin flip, and she died instead. Olivia asks what if these two people, both grieving for a version of each other in the exact same spot, are somehow causing this? Walter muses it could be some form of emotional quantum entanglement, or "spooky action at a distance," as Einstein put it. Two objects interact, even though they're far apart. And now it's happening again in Park Slope.
Broyles has Walter's ambering device set up in the Rosencrantz's lobby. Olivia explains the emotional quantum entanglement theory. They need to persuade Alice to break the connection and let go. Inside 6B, Alice looks at Other Derek and refuses to do as Olivia asks. The building shakes violently. Now Peter sees Other Derek too. And outside, everyone sees a shimmer of the Other Side. The vortex is starting! Peter tells Alice that she's already had a lifetime with the person she loves, and most people only dream of that. When Other Derek says that their daughters miss her, childless Alice realizes he's not her husband. He vanishes, and the shaking stops.
Alone together at the Bishops', Olivia and Peter toast disaster narrowly averted . . . or at least postponed. She mentions what he told Alice and says, "I want what you want." They kiss and head upstairs. Lights out.
On the Other Side, Lincoln and Bolivia are puzzled that the readings are normal at the Rosencrantz building's counterpart, despite Astrid's report of a Class 4 event there. After Bolivia briefly questions the man in 6B, Lincoln cancels the quarantine protocol. And Derek sits alone, looking at his own family album.