Newton gives Bolivia info on Olivia and her team and removes her sun tattoo with a laser. She asks about the job she needs done, and he explains he sent a team to "the site." He acts like he's in charge, but she coolly reminds him that he works for HER.
In Milton, Massachusetts, a frightened family is tied up in a home while a man watches TV. Down in the basement, his brother and another guy dig up a mysterious metal box. When they peek inside, the lamp fizzles and both men go catatonic. The guy from upstairs finds them with blood flowing out of their noses and their eyes turning white. He closes the box and runs upstairs. Now the TV is snowed out, and the family's bleeding too.
At the lab, Astrid reads William Bell's obituary to Walter while Broyles and Peter discuss the blueprints of the machine from the Other Side. Peter says that Walternate still needs a couple of the components. Plus, he's missing a really important piece: Peter. When Broyles asks Walter why the machine needs Peter to power it, Walter rants that it's dangerous. He leaves with Astrid, as Bolivia arrives to go for a drink with Peter.
Bolivia tells Peter she understands Walter's concern but agrees with Broyles that they need to figure out the weapon. "You've Really Got a Hold on Me" starts playing, and Bolivia says she loves this song. Peter's surprised at her interest in music. She says being Over There made her think about her worldview and her choices. She asks him to dance, and they flirt. Then her phone rings.
The team checks out the dead family in Milton, and Broyles says that he's getting fingerprints off the two dead diggers. But what were these guys after? Broyles thinks a third thief took whatever they dug up.
Bolivia tells Newton that two of his men died, as he had planned, but the third one took the device. Newton says that he only hired two men, and no one can withstand that thing. Well, someone did, says Bolivia, and they need to find him. Elsewhere, in a rumpled apartment, the third thief stares at the box.
Nina joins Peter and Walter for the reading of Bell's will at Massive Dynamic. Nina gets a small bell in a glass case, and both she and Walter get envelopes. Broyles phones Peter and asks if they're at Blake's apartment. Who's Blake? One of the dead thieves; they got a fingerprint hit on him this morning. Didn't Olivia call him?
At Blake's, Bolivia tells Peter she didn't call because she knew that Walter needed him. They smile at each other a lot. Bolivia says that she's going to talk to the landlord, but she really goes outside to call Newton. Blake's brother sits in his car with the box. He sees her badge and writes down her name.
Astrid asks Walter how the reading went. He takes a safety deposit box key out of his envelope, and she looks at the letter, which reads, "DON'T BE AFRAID TO CROSS THE LINE." Walter explains that Bell used to say that only those who risk going too far can know how far they can go. But Bell was Over There. He saw all that Walter destroyed. How could he tell Walter to cross the line? Astrid urges Walter to tell Peter his side of the story.
Suddenly, Walter thinks he knows what happened in Milton: Taken to an ultrasonic extreme, dissonant music could be fatal. You wouldn't hear any sound because the frequency would be too high. Peter wonders why the third man wasn't affected. Meanwhile, the third man goes to Bolivia's. She pulls her gun and orders him inside. Then she realizes that he's deaf. That's why he didn't die.
Walter pours his heart out to Peter, saying he couldn't let Peter die - again. But Peter snaps that Walter kidnapped him. Walter says he loves him, and he now understands that he should never have crossed the line. Peter says he can't talk about it and leaves.
Bolivia gives the box to Newton, who takes it to a subway station and pays a homeless dwarf to keep an eye on it for a minute. Then he splits.
Bolivia shoots Blake's bro - and Peter drops by. She lies about just getting out of the shower, drags the corpse into the bathroom, wets her hair, and lets him in. He says he just can't forgive Walter. He saw what Walter did - the quarantine zones, the damage. He obsesses over the drawing of him strapped into the doomsday machine. Is that his destiny, to destroy worlds too? Bolivia sees blood seeping out from under the bathroom door and starts making out with Peter to distract him. Then both their phones ring.
On the subway platform, Broyles tells the team that security cameras showed a small man walking into the tunnel with a metallic box. They realize the box is what the thieves dug up. So that Peter can retrieve it, Bolivia makes him temporarily deaf by firing her gun next to each of his ears. Peter finds the broken box and reports that it holds a piece of the weapon. He decides to disarm the device. Bolivia hears a train coming and races toward Peter. He stops the deadly signal, but the train is there! Bolivia pulls him to safety.
Afterward, Peter says maybe Walternate's agents are looking for the missing pieces Over Here. Broyles wonders why there'd be pieces here. Good question. Peter examines the device in the lab. Walter opens the safety deposit box. Later, he shows Astrid what Bell left him: Massive Dynamic!
In the secret room at the photo store, Bolivia types a message to Walternate: "Peter has first piece. He is actively engaged." Walternate responds: "Well done. Move on to phase two."