The egg is now in Zenith -- and when a man in a hazmat suit tries to pick it up, it zaps him to the ground. Back in chilly Chester's Mill, Melanie (Grace Victoria Cox) is screaming in agony as Sam (Eddie Cahill) and Junior (Alexander Koch) drive her to the high school; the medical clinic was damaged in the earlier earthquakes, and Rebecca (Karla Crome) has set up triage. Pauline (Sherry Stringfield) confronts Big Jim (Dean Norris) about his actions, and he insists he only dropped the egg to help stop her pain ... to get his family out from under the Dome. The pair finds Julia (Rachelle Lefevre) and Barbie (Mike Vogel), who explain what Big Jim's actions have resulted in: not only has the passage to Zenith closed, it's now a rocky ravine -- and it's killed Phil (Nicholas Strong) in the process. Joe (Colin Ford), Norrie (Mackenzie Lintz), and Hunter (Max Ehrich) brave the cold to check the Dome's edge; just as Joe touches it, it starts freezing over. Weirder still, it begins revolving ... and Joe's hand is stuck to it! Luckily, Hunter and Norrie help him get it free before it's too late.
The kids manage to get back to the school. Norrie wonders if any of this would've happened if she'd tried harder to keep the egg safe. Outside, Joe shows Rebecca what they've discovered -- that the Dome is rotating. Rebecca theorizes that it's bringing the colder upper atmosphere closer to the ground, which explains the drop in temperatures. Julia decides to take Barbie in the ambulance to pick up provisions from the Sweetbriar Rose. Pauline finally has a chance to talk with Melanie, and admits that she's back in Chester's Mill to make amends for what she did 25 years earlier. Meanwhile, as Barbie and Julia drive towards the diner, they hit a patch of slippery black ice -- and the ambulance crashes onto its side!
Barbie and Julia are lucky to be alive -- however, Julia's injured; a piece of metal has gouged itself into Julia's thigh. As the ambulance gets colder, Barbie realizes they can't remove the metal in case it hit an artery; staying put is the best of their "bad options." At the school, Big Jim asks Junior to advocate for him to his mother, but Junior refuses -- and also admits to knowing Pauline was alive for a while. Suddenly, Melanie has a seizure. Junior believes it's due to her connection with the egg; whatever they're doing to it in Zenith, it's happening to her too. Hunter starts asking questions about the egg, leading Joe to wonder why. Barbie does what he can to keep Julia warm; their prospects grow dimmer when the window above them cracks and falls, exposing them to the elements. Townsperson Tom races into the school with his frostbitten wife, but it's too late; she's dead. Just then, the school's generator runs out -- and Big Jim sets off outside to find more fuel.
Joe sneaks a look at Hunter's phone, finding his emails to Barbie's father Don. At the ambulance, Barbie believes they can use hypothermia to their advantage; it might slow Julia's heart enough that he can remove the metal in her leg and race her to safety. Big Jim goes to the lake to try and find more fuel, only to see Lyle (Dwight Yoakam) flailing helplessly in the water. Big Jim throws a buoy out and drags him to shore. In the warmth of Big Jim's car, Lyle says he saw the end of the world; flames a thousand feet high ... and it was beautiful. Meanwhile, Barbie manages to free Julia's leg and starts his trek to the diner.
Big Jim brings the fuel -- and Lyle -- to the school. Barbie gets Julia inside the diner and begins CPR. Miraculously, Julia comes to. The sun has started to rise -- and with it, Joe and Rebecca realize the temps are warming up. Pauline and Big Jim manage to bond a bit over old football trophies in the school hallway. Joe and Norrie find Hunter at the Dome's edge, talking via notes to one of Don's security people. They confront him, and he admits he's being blackmailed into helping Don -- but it all ends now. He's told the guards to stop messing with the egg, or else they'll all face catastrophe. Suddenly, there's a loud grinding noise -- and it's heard all over town. Melanie wakes up with a start and announces, "It's starting." Once the noise ends, Norrie realizes the Dome has stopped rotating. However, it begins to move toward them -- as if it's contracting. Is the Dome getting smaller?