In Milton, Massachusetts, a man, Joe, gets a pickaxe, prepare to go to the basement, and then considers the family that he and his confederates have tied up and gagged.
In the basement, Mitch and Blake are digging into the foundation and waiting for Joe to come down and help. They finally found a metallic box buried in the dirt and remove it. Blake suggests they take a look at it, but Mitch warns that they're not being paid to probe, and that Blake's curiosity got them into trouble in Texas. However, Mitch finally gives in and they open the box. They immediately start staring off into space, their eyes glazing over and their noses bleeding. A few seconds later, Joe comes down and realizes that something is wrong. He closes the box, goes upstairs, and discovers that the captive family is in the same condition.
At a secret location, Bolivia and Newton meet. While he removes her tattoo and tells her to read up on pop culture, she orders him to tell her the status of the site. Newton confirms that he hired a team to recover the item, and Bolivia reminds him that she's in charge of the operation.
At the lab, Astrid is reading William Bell's obituary to Walter, while Peter and Broyles review the blueprints to Secretary Bishop's doomsday device. Broyles wonder why it's configured for Peter, but Walter insists that it's too dangerous to even contemplate. He goes to the market as Bolivia arrives, and Broyles asks Peter to get Walter back on track. Peter echoes his father's concerns and then leave with Bolivia, unaware of who she truly is. They go to a bar for drinks, and Bolivia agrees with Broyles. They discuss the music on the jukebox, and Peter admits that he's surprised since she's never discussed music with him before. Bolivia claims that she's learned to embrace new experiences since seeing the Other Side, and invites Peter to dance with her. As they dance, he admits that it was strange meeting the other Olivia, but admits that he thinks she looks sexy as a redhead.
Bolivia and Peter are called to investigate the house in Milton. The family and the robbers are dead, and Walter points out that the blood from their ears and noses is too bright. Broyles is unable to ID the two robbers in the basement, and Walter explains that they went into a vegetative state before they died some time later. They realize that whatever the men dug up is gone, and figure that a third man was present, and somehow survived.
The next day, Bolivia meets with Newton and tells him what happened. He explains that he only hired two men, the two dead robbers, and Bolivia tells Newton to find the third man and discover why he's immune.
At his apartment, Joe contemplates the stolen box.
As Walter conducts an autopsy at the lab, Peter arrives to pick him up. Walter worries that he's underdressed for the occasion, but Astrid assures him that he's fine. Peter then takes Walter to Massive Dynamic for the reading of Bell's will. Walter hugs Nina, who is also present, and expresses his condolences. At the reading, Nina receives a memento from the time she spent with Bell in Tuscany, and Walter gets an envelope. Afterward, Peter asks what is in the envelope, but Walter says he's not going to tell him for now. Broyles calls Peter and tells them that they used fingerprints to identify one of the robbers, Blake. He wonders why Walter and Peter aren't at Blake's apartment, and explains that Bolivia is at the address and was supposed to call them.
Peter arrives at the apartment as Bolivia searches for clues. She claims that she didn't call him because then he'd feel obligated to leave Walter. They realize that a second person lived there. While Peter checks the apartment, Bolivia goes outside and calls Newton to tell him to find the third man. Across the street, Joe watches her and writes down her name despite the fact he can't possibly hear her.
Walter goes back to the lab and informs Astrid that Bell's gift to him was a safety deposit box key. There's also a letter, telling Walter not to be afraid to cross the line. Walter doesn't understand why Bell would tell him to take risks given that his impetuous kidnapping of the other Peter is what set off the destruction on the Other Side. Astrid encourages Walter to tell Peter what he had to do to save him, but Walter insists that he's waiting for the right time. When Astrid tries to pursue the matter, Walter is distracted when he realizes the dead men have severe inner ear trauma.
When Peter comes back to the lab, Walter dons his brain-scanning helmet and uses music to demonstrate that it can affect neural patterns. He then hypothesizes that the men were exposed to an extreme ultrasonic wave that induced the vegetative stance and ultimately killed them. Walter concludes that the missing man used some kind of protective earpieces to protect himself. While Peter calls Broyles to have the FBI look out for ultrasonic incidents, Astrid tells Walter to talk to his son.
Bolivia is at Olivia's homing going over Olivia's files when Joe shows up at her doorsteps. She aims her gun at him and tells him to put the box down, and then realizes that he's deaf.
Walter approaches Peter in the lab office and tries to explain what happened. He explains that when "his" Peter died, he lost all hope and only his wife and his window to the Other Side kept him going. When he saw the Other Peter and knew he was going to die, he couldn't stand by and let that happen. Peter insists that he was wrong to kidnap him, and Walter apologizes. Peter refuses to talk about it further and leaves.
Bolivia summons Newton to her apartment and tells him that Joe saw her badge at Blake's apartment and contacted her in the hopes of turning the box over to the government. Newton offers to dispose of Joe, but Bolivia tells him to do his job. He leaves with the box and Bolivia apologizes to Joe before shooting him in the head. She starts to move the body, but Peter arrives at her doorstep. She hides Joe's corpse in the bathroom and claims she's in the shower. She then answers the door and Peter tells her what Walter said. He admits that he can't bring himself to accept Walter's apology, and worries that he may destroy a world just like Walter did. Bolivia sees Joe's blood leaking out from under the bathroom door and offers to kiss Peter so she can distract him.
At a train station, Newton sits down on a bench. When a homeless man comments on the box, Newton refuses to say what's in it and pays the man to watch it while he goes to the restroom.
Broyles calls Peter and Bolivia, interrupting her before she can do anything further. They go to the train station where five people have gone into a trance. The homeless man picked up the box and walked down the tracks to the next station. Broyles wants to send a bomb squad, but Peter warns that they don't know what it is and they could be putting the squad members art risk. He offers to go instead, and Walter warns that it's too dangerous. Peter asks him for a way to protect himself, and his father has an idea. He has Bolivia fire two rounds, one past each of Peter's ears.
Deafened, Peter runs down the tracks and finds the homeless man, now in a vegetative trance. As Peter looks on, the man's head explodes. Peter tries to close the box and realizes it's part of the weapon he saw on the Other Side. The box is damaged from when the homeless man dropped it, and Peter tries to disarm it before his hearing returns. Back at the station, Bolivia hears an oncoming train and runs down the tracks to help Peter. Peter defuses the device and Bolivia pulls him out of the way before the train can hit him.
Back at the station, Walter tells them that the homeless man's fillings exploded due to the ultrasonics. Broyles wonders why there are any weapon pieces on this side, and Peter admits that it's hard to tell what the people on the Other Side have planned. As Peter takes the box back to the lab, Broyles thanks Walter for his idea. Walter removes the safe deposit box key and considers it carefully.
Later, Walter goes to the bank and removes the contents of the box. He takes the contents back to the lab and explains to Astrid that Bell left him his shares of Massive Dynamic. Walter now owns the company.
Peter studies the blueprints for the weapon along with the box, and pays careful attention to the human figure strapped into it.
Bolivia goes to the store and makes her report via typewriter. She tells her superiors that Peter is now engaged, and they respond by telling her to go to work on Walter.
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