In a Boston pawn shop, Peter buys a necklace and is confronted by an Observer. He struggles to resist being read and barely escapes.
At Harvard, Astrid and Walter retrieve videotape No. 2 from the amber. Peter returns and says the Observer got an image of Etta from him. She means to teach them to resist readings by keeping a labyrinth of planned thoughts in their minds, but learning that takes time.
Peter gives Etta the necklace, to replace the one they used in building the laser.
Captain Windmark shows Phillip Broyles the footage of Peter and wonders why a fugitive would risk capture to obtain something so . . . unexceptional. He says that, two days ago, one of Broyles' men failed a security test - and is probably with the resistance.
On the videotape, Walter says you must accept the reversibility of all phenomena. But most of the rest is garbled. He displays a metal tube containing plans they must follow to the letter. It's hidden as he would hide his most prized possessions. The tape rips, but Walter knows where to go: the subway platform beneath Newark Penn Station.
Every major access point to Manhattan has an Observer checkpoint. They'll need a plan.
Walter de-ambers a trapdoor to reveal a basement stuffed with his secret "cold storage" of all the Fringe events: the porcupine man, the window to the Other Side, the toxin that suffocates people by sealing all their orifices, etc. Time to create their own Fringe event.
When an Observer interrogates the undercover resistance member, he extracts a code name: the Dove. The Dove's identity is a mystery.
Broyles secretly checks his weapon as the Observer enters his office. The Observer, who glimpsed a reference to Harvard in the agent's mind, notes Broyles' relationship with the fugitives. Broyles says that was a long time ago. The Observer leaves, and Broyles releases his grip on his sidearm.
Etta strings the spent bullet onto her new chain, explaining to Olivia that she found it in their old house years ago. Olivia says Peter called it "the bullet that saved the world" - the one Walter used to stop William Bell (Season 4, Episode 22, "Brave New World Part 2").
Etta receives a message: The lab's compromised. Broyles leaves his office, pocketing his phone. They re-amber the lab and depart with the gear for their plan.
When troops find the unoccupied, ambered lab, Windmark concludes that the reading from the resistance fighter was deceptive. Somehow, Etta hid her thoughts. Perhaps others can as well.
Walter, Peter, Etta and Olivia attack the station guards with the aforementioned toxin (Season 1, Episode 14, "Ability"). They retrieve the tube, but a dying Loyalist attaches a tracker to their car.
Walter examines the plans. It's some kind of physics, in his handwriting, but he doesn't understand it. Then Broyles drives up for an emotional reunion. He explains that Etta recruited him into the resistance - and taught him to hide his thoughts.
Broyles provides weapons, including antimatter batons that, once armed, can't be deactivated. But the Observers have caught up! Broyles departs with the tube. The team flees on foot and gets separated in a warehouse complex.
Windmark captures Etta. He spots the necklace and realizes Peter bought it for her. He asks, "For what purpose?" After reading her and seeing Peter, he concludes it's for love. Etta tries to stab him, but he's too quick. You never know when to give up, Windmark says . . . and shoots her.
The others rush to the mortally wounded Etta. Windmark is gone. Etta's activated an antimatter baton, forcing them to leave her. Peter sobs that he can't, not again. But they have to go. Olivia takes the necklace.
Windmark says the team will return for Etta, because of love. When they find her alone, he notices the necklace is missing. He teleports out before the baton detonates.
Nearby, Walter says they need to leave. Olivia looks at the bullet. Peter stares at the complex. And they go.