At a train station, about two dozen afternoon commuters spontaneously combust. Others stand frozen in fear. One woman tells the others not to move, or they'll die.
Meanwhile, Peter and Olivia lounge in bed, looking at house ads and contemplating baby-making. Their phones go off.
Walter shouts instructions while a hazmat team checks out the scene. Astrid buttons his coat. He grumbles that she doesn't need to mother-hen him - he's quite capable of looking after himself. Astrid knows, but maybe she likes doing it. Walter smiles.
Inside the station, Walter takes a blood sample from a young woman named Jessica. She's obviously scared but calm, even bantering with him. He notices smudges on her fingertips, which she thinks came from the escalator.
The escalator machinery has a strange device attached, which Walter says is generating nanites: microscopic self-replicating robotics. They're activated by their hosts' movement and become more sensitive the longer they're in the bloodstream. Eventually, the slightest exertion causes spontaneous combustion.
Jessica, an ER nurse, agrees to be transported to Harvard so the Bishops can devise a cure. She phones her ex and has him pick up their daughter. When her temperature spikes, Olivia takes her hand. The power flickers out. Olivia sweats, and Jessica cools down. The power comes back on. Jessica asks how Olivia did that? No idea.
Walter thinks the Cortexiphan has given Olivia certain kinetic powers. Perhaps in this case she slowed molecules down, cooling Jessica off. They finish the cure.
Examining the nanites, Walter is stunned that they have a chimeric structure. Astrid reports that Jones is behind this; Broyles has surveillance footage of him sabotaging the escalator. Walter says Jones didn't create these. Only one person would construct this particular pattern. Who?
Jones enters a dimly lit office and reports that Agent Dunham has interfered again. William Bell chuckles and says, "Don't confuse a winning move with a winning game."
Jones asks about Bell's chess board, and he says it's been about 20 years since the last move. In this game, the most important skill is patience. The board changes, but very slowly. The art of chess is knowing when a piece is most valuable, and then being willing to sacrifice it. For in the vacuum created by that loss, opportunity abounds, influences maximize, and desire becomes destiny. Here, the most valuable piece is the bishop. Therefore, for the game to be won . . . Jones finishes: The bishop must be sacrificed. He's on it.
Walter tells Nina that William Bell is alive. He should've known: Jones' plans were too ingenious; they had to be Belly's. Nina says Jones could've copied William's research. Walter huffs that the nanites were the work of a master, not an imposter!
Nina informs Olivia that Bell died in a car accident on Christmas seven years ago, not New Year's Day as Walter says. Walter insists Bell visited St. Claire's Hospital on New Year's Eve 2005, to say goodbye. Nina shouts that the crash wasn't an accident. William had lymphoma. He wanted to go out on his own terms, and he did. He's dead. Period. Walter softens, but Nina says the man she knew wouldn't try to destroy a universe! That sounds like ANOTHER man she knew. Fine, Walter will prove it.
But the St. Claire's 2005 visitors' logbook shows no William Bell. Walter sniffs a page, then tastes it. Can he borrow this?
At home that night, Olivia talks about Jessica's daughter almost becoming an orphan, and wonders how she and Peter can have a normal life. This power she has is terrifying. Peter reassures, saying that after all they've been through, he won't lose her again. Suddenly, a bright light shines outside.
Meanwhile, on a Beacon Hill rooftop, Broyles watches a column of light burn through a building.
Walter explains that Jones is reflecting sunlight off something, like one of those disco balls, and focusing it, like a magnifying glass. Beacon Hill sits above a subterranean oil reservoir, so this sun beam could set Boston on fire from below.
Walter directs Olivia and Peter to the antennae of two private satellites Jones is controlling - the proverbial disco balls. They're on adjacent rooftops, so each takes a building as Jones watches nearby.
Hoping to regrow fingerprints on a logbook page, Walter does some weird baking that activates a little-known Cortexiphan side effect: temporary tissue regeneration. Instead he finds almond oil on the paper. Belly was obsessed with Chilean almonds, and bought them from the importers wholesale. He and Astrid head to A1 Imports to find Belly.
Peter and Olivia turn off the beam, but Jones attacks Peter with a crowbar! Olivia thrusts her shoulder back, and the motion continues in Peter, throwing Jones off. She's using her kinetic power. Olivia/Peter knocks Jones into the antenna, and he fries. Dying, Jones says he got it wrong: HE was the sacrifice. He was the bishop.
At Boston Harbor, Astrid and Walter learn that A1 Imports is out of business. Walter hears animal noises and heads inside as she follows.
Armed guards confront them. Astrid says she's FBI, and a guard trains his semiautomatic on her. She kicks the gun from his hands. She grabs Walter, and they flee under fire. Astrid shoots one pursuer, but they're cut off by another, who shoots her in the chest. Walter catches Astrid as she falls. She looks at him and says, "I tried." Walter stares at the blood and caresses her cheek, distraught.
"What a wonderful surprise!" booms a cheerful voice. Bell approaches, saying he's not sure he ever thought he would see Walter again. "Hello, old friend."