At Park Slope in Brooklyn, Chris and Sylvia are going to an apartment party at the Rosencrantz Building. As they wait for an elevator, a woman, Mrs. Marcello comes down the stairs with her luggage. She tells them good luck using the elevator and goes outside. The doorman, Jimmy Smith, asks if she's leaving, and Mrs. Marcello insists that she can't spend another sleepless night in the building.
The couple arrives at the party and the hostess, Kim, talks to Sylvia about Chris. The blender comes on by itself and Kim admits that it's not the first time appliances have turned on by themselves. Sylvia starts to choke on an appetizer and they call Chris in to get her medication.
As Mrs. Marcello gets in her cab, bodies crash to the pavement behind her as the partygoers fall to their deaths.
Walter is at home making breakfast, and explains to Peter that he misses Olivia since they haven't seen her in the last couple of weeks since they haven't had any cases. Peter insists that it's none of Walter's business, and tells him not to force anything. Olivia arrives and Walter invites her in, and she quickly realizes he's set her up to spend time with Peter. As Walter slips out, Peter suggests that they talk about what is bothering her. Olivia tells him that she knows he still has feelings for her counterpart, Bolivia, and he's not being honest with her. Peter insists that he didn't tell her because he knows Olivia has trouble with personal issues. He explains that he had a chance to see what it would be like for the two of them to be together, and wonders who is keeping them apart now.
Before they can discuss matters further, Peter and Olivia are notified of the incident at the apartment. They arrive with Walter, and Broyles explains that six people jumped to their deaths. There's no structural damage to the balcony or other indications of why they fell, and the patio furniture fell with them. Olivia talks to Jimmy, who talks about how he was helping Mrs. Marcello into the cab when everyone fell. He suggests that it's true that the building is haunted. Meanwhile, an older woman, Alice Merchant, watches the authorities examine the crime scene from her 6B apartment window.
Kim and her boyfriend Rick tell Broyles that they dealt with Sylvia, and the six partygoers leaped to their deaths when they weren't looking.
Peter and Walter examine the balcony and realize that the people who fell to their deaths must have slipped through the solid floor of the balcony. Olivia informs them that the residents think the building is haunted. Meanwhile, Walter flips a coin repeatedly and tells Peter and Olivia that it has come up heads ten times. He theorizes that their world is starting to come apart and it's starting at the Rosencrantz Building.
At the lab, Walter looks for a seismograph to measure microquakes, and Astrid finally goes to get it. He snaps at the others and notes that the universe is collapsing, and the hole they're dealing with could lead to a vortex. He wants Peter and Olivia to gather as much data as possible from the Rosencrantz Building. Once they go, he tells Astrid to bring him the file on the commuter bus chemical attack from three years ago. When she wonders why, he snaps at her for questioning him and she hastens to obey.
At the building, Peter and Olivia set up their equipment. They call Walter, who tells them to stay there for last-second calibrations. As they wait, Olivia wonders if it's the end of the world. Peter suggests they go to a nearby bar and get out of the cold. As they go, the old woman, Alice Merchant, enters the building. She checks her watch and enters the elevator, goes to her apartment, and takes a photo album off her shelf.
In the bar, Olivia talks about knowing what it feels like to experience what Bolivia felt. She leans forward and kisses him, but then draws back and says she needs to get some air. Olivia goes outside on the street and Peter comes out after her. She explains that when they kissed, he glimmered, and she wonders if she's incapable of lowering her defenses. As they talk, Olivia looks up and sees a glimmer from 6B.
In her apartment, Mrs. Merchant is looking at her photo album when a golden light fills the apartment.
Peter and Olivia run up to the apartment and break in, and find Mrs. Merchant gazing at a ghostly figure of an older man. She explains that the ghost is her husband Derek.
Later, Walter arrives and checks for radiation readings. He insists that there's no such thing as ghosts, although William Bell disagreed. Meanwhile, Olivia talks to Mrs. Merchant, who confirms that she's been seeing her husband's ghost for two months. She shows Olivia the photo album and explains that Derek was an amateur photographer, who took hundreds of photos. They traveled a lot because they never had children. Derek died when he flipped a coin to see which of them would change a fuse. He lost, there was a short in the wiring, and he died instantly. Mrs. Merchant started seeing him a few days after he died, when she was ready to die rather than be without him. Walter comes in and confirms that Derek owned the apartment for 40 years, and that Mrs. Merchant moved in after they were married.
Outside, Walter explains that Derek's counterpart on the Other Side most likely owns the same apartment. The universe is breaking apart, and the apartment is the center of the rip. He worries that if the rip is so thin that Mrs. Merchant can see through the rip, then things are very dangerous.
Back at the lab, Walter demonstrates how the barrier between universes will eventually shatter, creating a vortex that will suck in everything nearby on This Side. Astrid arrives with the files on the commuter bus attack, and Walter explains that they would do the same thing as their counterparts on the Other Side: use the amber substance to block the gap. The information has been sent to Massive Dynamic. They meet with Nina, who explains that they've been doing work with the amber. Walter wants them to encase the entire block in amber to stop the breach from becoming a vortex. The others warn that it could cause a panic, but Walter insists that there's no other choice.
The team meet and Olivia explains the procedure that their counterparts use to disperse the amber and seal the rifts. Broyles goes to tell the President what they know, and Peter suggests that there must be another way. He wants to determine why a breach is forming at the Rosencrantz Building, and they pull up information on all of the incidents there.
In the lab, Brandon replicates the compound that Walter is looking for. Nina checks in and Walter admits that he can understand the decision that his counterpart, Walternate, came to make.
Olivia goes over the building information, while Peter focuses on why Alice can see the Other Side. He figures that on the Other Side, Alice lost the coin flip and died. They go to Walter and Olivia suggests that the two individuals on either side of the breach, yearning for their counterpart, are creating the gap. Walter admits that it's possible and starts to test, while Astrid calls to tell them that there's more seismic activity at the Rosencrantz.
The team arrives at the Rosencrantz and explain to Broyles that emotions are the key to seeing through to the Other Side, and creating the breach. Alice refuses to leave, and Walter explains that it doesn't make a difference how far away she is. She needs to break the connection on her own, and Olivia says that they need to convince Alice that the person she is seeing isn't her husband. Peter and Olivia go in to talk to her, and Broyles tells them to get out as soon as he alerts them that they're preparing the amber encasement.
Olivia and Peter go to the apartment and find Alice contemplating the ghost of her husband. She tells them to get out, but Olivia tells Alice that she has to let her husband go before the rift opens. Olivia tries to explain the concept of parallel worlds, and how the people on the balcony died because Alice couldn't let go of her counterpart. The other Derek calls out to Alice, and he becomes more "real," enabling Peter to see him.
In the street, everyone can see the shimmer. Broyles orders Peter and Olivia to get out, and Walter warns that the vortex is starting to form. They contemplate the remote device for the amber encasement, and Walter tells Broyles how to activate it. Broyles arms the device and gives Peter and Olivia a direct order to evacuate.
Olivia tries to get through to Alice without success. Peter steps in and tells Alice that she has to give Derek up, and she's already had a lifetime with the person she loves. Meanwhile, the other Derek says that he and the girls miss her, and Alice realizes that he's not "her" Derek. She tells the other Derek that his Alice is gone, and he fades away as the vortex disappears.
Later, Alice admits that she's not sure she'll ever understand what happened, but admits that with everything she's seen, she wonders if she might see Derek again some day.
At Massive Dynamic, Walter is in his office looking out over the city when Nina comes in. She says that he should be proud that he saved so many lives, but Walter warns that what they experienced is a vision of things to come. Eventually the cracks will open, and spread, and cover the world. The best solution that Walter has is the amber, and he realizes that it won't be enough once the universes unravel. He admits that he doesn't know what to do, and Nina says that he needs to learn.
Olivia comes to see Peter at home and brings a bottle to share a drink. As they toast to disaster averted, Olivia admits that she wants what he wants, and he asks what they should do about it. They kiss, she assures him that he's not glowing, and they go to the bedroom.
On the Other Side at the Rosencrantz, Lincoln and Bolivia examine the building but discover that their initial warnings of a Class 4 event are now negative. They visit apartment 6B and talk to Derek Merchant. He says that he didn't notice anything and he lives alone since his wife died. As Lincoln and Bolivia go, Derek looks at his photo album... alone.