At Massive Dynamic Walter and Kevin the security guard share a bong and Walter regales his new friend with stories of how he ended up in bed with Yoko Ono during the 70s. Walter admits that he hasn’t accomplished much as head of Massive Dynamic, and Kevin assures him that he’s much cooler than William Bell ever was. As they watch the security monitors, Walter comments on the patterns of people moving through the hallways, but notices one old-fashioned wooden door that no one enters. Kevin explains that it’s the door to Bell’s old office.
Two hours later, Walter enters Nina’s office with a cart filled with Bell’s old files. He explains to her that he’s trying to stop the two worlds from colliding, and since Peter and Olivia are now together, he has a personal reminder of what will happen if he fails. When Nina wonders what that has to do with Bell’s old files, Walter explains that he’s revising their work together and trying to come up with a way to think the way that he used to, when anything was possible.
At the Massachusetts Metal Depository, two masked men defy gravity by climbing down the side of the building after breaking in. When they reach the “bottom,” they put on weighted boots to maintain their footing, but a security guard spots them. The first man, Koenig, goes for his gun and the security guard is forced to shoot him, while the second man, Bill, escapes in their car. The security guard is shocked to see Koenig’s body, including the splattered blood, drift up into the air.
Peter is working at a private office at the Harvard Engineering Building, linking the memory discs from the murdered shapeshifters together. He manages to tap into the hidden information on them, but is unable to decipher it. Olivia calls him from her car to invite him to a street fair, and offers to pick him up at his home. Peter lies and says that he’s working out at the gym, and says that he’ll meet her at the house. As Olivia hangs up, she gets a text message from Broyles summoning the team to the Depository. When they arrive, they’re surprised to see Koenig floating off the ground. As the police pull him down with a line, Olivia talks to the security guard and gets a description of the second man. They find a key card but the security guard confirms that they don’t use that model in the Depository. Peter checks Koenig’s discarded boots and confirms that they are weighted, while Walter examines the body and discovers atrophy of the leg muscles, but not the upper body. He admits that the dissimilar atrophy would be impossible if Koenig lived in a zero-g environment. The security guard finally confirms that the only thing stolen from the Depository was osmium, the heaviest element on the planet.
At Frost Aerodynamics, Dr. Krick is leaving with an associate when Bill calls him over in the parking garage. Bill tells him that Koenig was shot trying to escape, and he’s suffering from nausea. Krick tells Bill to go to the lab and then leaves separately.
At Harvard, Peter searches Bell’s files for references to anti-gravity, while Walter confirms there are no lighter elements in Koenig’s still-floating body. He does determine that Koenig has a low white-cell count, meaning some foreign substance is attacking the body’s defenses. They realize that the anti-gravity effect is wearing off and Koenig’s corpse is slowly dropping to the ground. Olivia arrives to inform them that they’re still trying to confirm the other thief’s identity, but they’ve traced the keycard to a warehouse in Allston. She affectionately invites Peter to go with her, and Walter smiles at the thought of them together.
At the warehouse, Krick uses his key card to gain entrance, and discovers that Bill is bleeding from the eyes. Bill wonders what is going on, and notes that Krick said that once they had more of the osmium, the anti-gravity effects would be permanent. Krick mixes the osmium with another substance and warns that they can’t defy Mother Nature, but they’ll soon be able to eliminate the side effects. Before he can give Bill an injection of the new mixture, the man dies.
At Harvard, Walter and Astrid are watching Koenig’s corpse as it suddenly falls to the ground. Walter is puzzled as to why the rate of anti-gravity wearing off is inconsistent, and tells Astrid to move the body. She irritably does so, only to discover that it is far heavier than it should be. Walter has her take another blood sample and test for osmium.
As they drive to the warehouse, Olivia suggests that they play a game of full disclosure and admit what they dislike about the other. She insists that it’s a matter of trust, but Peter is hesitant.
Krick is dissecting Bill’s corpse when he checks the monitors and sees Peter and Olivia enter the building. They enter the lab area and find Bill’s corpse, but Krick is long gone. Checking around, they find a walk-in freezer filled with other dissected corpses.
Walter arrives to check out the corpses and confirms that they all died of osmium poisoning. Each corpse has injection marks, and the bodies were cut up after they died. Broyles reports that the local police have found eight discarded wheelchairs, and the histories of the victims show that they all had long-term muscular dystrophy. A chagrined Walter admits that would explain the inconsistent atrophy, and blames himself for not realizing it sooner.
Krick goes to a gym where his son Michael is playing wheelchair basketball. As he watches, he notices another wheelchair-bound teenager, Vince, watching from the stands. Krick asks why he isn’t playing, and Vince admits that he’s too ill to play. The doctor offers the change to let him play, and much more.
At Harvard, Walter is examining pieces of solidified osmium taken from Koenig and Bill, while Peter and Olivia are unable to find a connection between the other eight men. Peter suggests that they go for pizza, and Olivia agrees. The find Nina in the hallway with a file for Peter, and she compliments them on being together. When Olivia wonders what the file is, Peter casually dismisses it as information on the shapeshifters. Olivia steps away to take a phone call and Nina tells Peter that he’s made the right decision to be with Olivia.
In the lab, an agitated Walter insists to Astrid that whoever is behind the anti-gravity is tampering with the fundamental forces of the universe. He puts a mint into a Coke bottle to demonstrate, causing a geyser just as Nina comes in. He tells her that he can’t save the two worlds without Bell, and shows her a file on Bell’s research into “soul magnets.” According to the files, Bell believed that microscopic magnets placed into a host body would allow the return of the “soul,” the person’s consciousness that lives on after death. Walter wants to make Bell’s theory a reality and bring his old friend back, but Nina assures him that his imagination is his primary asset, and that he won't fail because he can't.
Krick meets privately with Vince and gives him an injection of his osmium formula. The teenager rises out of his wheelchair and drifts toward the ceiling, and Krick quickly provides a pair of weighted boots to keep him anchored. The doctor warns that the effect is temporary and he needs more of the necessary elements. Vince offers to help him get them.
At Harvard, Astrid is surprised to discover that Walter is using liquid nitrogen to melt the solidified osmium. He explains that since the person responsible reversed the laws of physics, he speculated correctly that using cold instead of heat would allow him to melt the osmium. When it melts, a second white substance is filtered out and Walter has Astrid call Olivia.
That night, Krick helps his son out of his wheelchair and into bed. The scientist prepares to leave, saying he has work to do, and that it’s a major breakthrough that will change everything. Michael assures him that he has never failed before, and won’t fail this time.
At the lab, Walter identifies the second substance as lutetium, another rare super-dense element. He points out that it’s found in meteorites, and Astrid notes that the Museum of Science has a meteorite display.
Vince uses his anti-gravity power to enter the museum via the unsecured skylight. He then bypasses the alarm and lets Krick in. The scientist extracts the lutetium from the meteorites, but Peter and Olivia arrive with the museum staff. Krick abandons Vince, leaving him adrift, but Olivia quickly captures him. As Vince floats up toward the skylight and the open sky beyond, Peter manages to tackle him and bring him down to earth.
Later, Walter and Peter bring Michael to see his father. Krick insists that he did what he did to help people, and to fix Michael. Michael insists that he isn’t broken, and that he was happy with a father that he knew loved him. He angrily leaves and Peter goes after him, and Walter warns Krick that Icarus also gave his son the power of flight, but it eventually cost Daedalus his life. He asks Krick how he was able to reverse the laws of physics, and the scientist explains that he has no idea how. He was experimenting with two heavy elements as part of a military contract to build an ultralight allow for airplane manufacture, and stumbled upon the combination by accident. Krick admits that not only does he not know how his formula works, but that he has no idea how it could work.
Walter goes to see Nina and explains what Krick told him. He informs her that Krick unwittingly took advantage of the breakdown in physics that Walter set in motion 25 years ago by crossing universes. Nina points out that Walter is taking it well, and he says that he has finally found a way to bring Bell back to help them stop the breakdown.
Peter takes Olivia to his private office and explains that he doesn’t want the FBI taking his data, and Walter would be too protective. He’s the only one that he trusts with the information he’s gathered on the shapeshifters.
Walter gets the antique bell that William Bell left Nina in his will, and explains that its vibrations should suffice to bring back Bell’s consciousness, his “soul.” He rings the bell and stares expectantly at Nina, but she insists that she’s still herself. Walter says that once Bell has returned, his consciousness will eventually find them, and they both look expectantly at the office door.
Peter takes Olivia into his office and shows her the information he’s compiled on the shapeshifters and the Machine. When she sees the memory discs, she realizes that he’s the one who killed the shapeshifters to obtain the information. As Olivia looks at them, she hears faint ringing noise. Peter says that he’s extracted the information but can’t decrypt it, and Olivia says in a distinctive different voice that the decoder key is in her office. Her boyfriend is confused, assuming she means her FBI office, but “Olivia” explains that it’s in Bell’s office at Massive Dynamic, and says that it’s good to see Peter again.