As the Dome collapses, Joe, Norrie, and Hunter find a way out. Meanwhile, Big Jim loses someone close to him and tries to make a deal with the Dome.
With the egg gone, the Dome starts contracting, threatening everyone within. Barbie contacts his father and demands the egg, revealing the presence of his half-sister. Meanwhile, Melanie's condition grows worse and Big Jim works with Pauline to create a new painting that will show them the way.
The temperatures inside the Dome plummet and Julia and Barbie go to save the food, while Big Jim looks for fuel to power the generator at the high school. Meanwhile, Melanie begins to suffer and Junior realizes that her health is tied to the egg.
Big Jim is reunited with the wife that he believes is dead, while Barbie and Julia are reunited and realize that the egg is missing. Meanwhile, Joe and Norrie meet Hunter and set out to find the egg, as the temperature beneath the Dome begins to drop.
The mercenaries capture Barbie and demand that he get the egg for them. Meanwhile, Sam, Pauline, and Lyle try to track down the red door from Pauline's visions, and Big Jim makes a deal with the mercenaries guarding the Dome.
Barbie makes contact with a mysterious hacker who knows that Barbie's father Don is playing a dangerous game. Meanwhile, new sheriff Big Jim suspects that someone is after him and enlists Junior and Rebecca to help him.
When Barbie tries to recover Sam's body, he is pulled into the chasm and finds himself outside the Dome. He sets out to find the one man who can help him get back into the Dome with Julia: his father, Don. Meanwhile, Julia tries to conceal that Barbie is apparently dead but Big Jim finds out and uses the information for his own purposes.moreless
Barbie and Sam investigate the tunnel behind Melanie's locker at the school, but an explosion cuts them off from the others. A dust storm comes up and Julia must choose whether to help the town or try and rescue Barbie. Meanwhile, Joe and the other three hands recover the egg from the lake.moreless
Julia takes over as the new leader of Chester's Mill, after the town becomes divided over Big Jim and Rebecca's population-control plan. Meanwhile, Joe and Norrie help Melanie search for clues about her identity at the dome wall.
Barbie and Julia take opposing sides when Big Jim and Rebecca take extreme steps to extend the town's resources. Meanwhile, the mystery of Melanie Cross deepens.
Acid rain threatens the residents of Chester's Mill, further endangering their lives. Meanwhile, Rebecca and Lyle argue over the reason for the Dome's existence.
Barbie risks his life to help Rebecca save the Chester's Mill food supply when she discovers an infestation of butterfly eggs on the town's crops.
Before Big Jim can execute Barbie in the town square, an electromagnetic pulse fells many of the townspeople. Meanwhile, Julia rescues a woman who falls into the lake out of nowhere, and Big Jim receives two visitors who try to convince him to see the error of his ways.