Over at Formerly Harvard Lab, Walter and Astrid have managed to free Tape 8, on which Video Walter is explaining that they need to go to a scrapyard in Fitchburg, forty-six miles northwest of Boston, to get an industrial-size electromagnet, the kind used in automobile junking. Thankfully we appear to have largely dispensed with the "tape quality is bad thanks to the amber" complication most of the early tape rescues had. Olivia comes in -- having gone through the secret passage, of course -- and looks somber enough as she sets her bag down that Walter asks what's wrong.
So she explains to them, and shows them the tech Anil gave her. Walter is completely baffled, and Olivia doesn't know when Peter did it. Walter asks her what the manifestations are, and Olivia tells him that Peter is reading time like the Observers do and he knows what she's going to say before she says it (that would be super-annoying). "Walter, he's convinced that this is the only way to beat them," she says, and wants him to find out what it's doing to him. Walter, examining it with a magnifying glass, promises to start running diagnostics right away, but the danged thing needs to integrated with organic material. "I need to see how it interacts with an actual brain," he says. Astrid -- understandably concerned, given she's last to appear in the credits and is therefore most expendable -- asks whose brain Walter has in mind (no pun intended, I imagine). Walter thinks about it a moment before suggesting "my porcupine man's." He preserved the brain in formaldehyde, and Astrid goes to fetch it.
And then Peter's calling Olivia, and Walter asks to take the call, so Olivia hands over her comm. Walter asks Peter where he is -- Peter tells him he's in New York -- and says he needs to come back to the lab: "What you've done, son, is extremely dangerous," says Walter. Peter's not sweating it; he only called to warn them not to go back to Etta's apartment, because it's been compromised. (Took 'em long enough to get there, really.)
Walter pleads with Peter to come back to the lab, not just because they don't know what the tech is doing -- Peter assures Walter that he's in complete control, not that Walter believes it -- but because Walter wants Peter to keep his promise to be there for him: "Do you remember? To keep me from slipping? I need you. I'm begging you. Please come back in and let me run some tests," says Walter.