Barbie’s fate lies in Big Jim’s hands, and the Dome presents a new threat when it becomes magnetized. Meanwhile, Julia seeks out the help of a stranger to save the life of a mysterious girl who may hold clues to origin of the Dome.

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.

When tensions in Chester’s Mill continue to rise as resources dwindle, Big Jim holds a census in order to forecast how long the town can continue to exist under the dire conditions. Meanwhile, a rainstorm brings much-needed water until it changes to acid rain, threatening the lives of everyone it touches. Also, Rebecca and Lyle butt heads over the reasons for the dome’s existence.

As conditions in Chester's Mill worsen, Big Jim and Rebecca consider resorting to the extreme measure of population control, which drives a wedge between Barbie and Julia. Meanwhile, clues to Melanie's past and her connection to the Dome are revealed.

Julia takes over as the leader of Chester’s Mill after the town becomes divided in the wake of Big Jim and Rebecca’s plans for population control. Meanwhile, Joe and Norrie help Melanie search for more clues about her identity at the Dome wall.

When Barbie and Sam set out to investigate a mysterious tunnel, a cave-in severs their path back to Chester’s Mill. Meanwhile, Julia and Big Jim face off in a struggle for power as a dust storm rages in the town.

When Barbie descends into the unknown abyss in the mysterious tunnel to look for Sam, he discovers a world that is familiar but filled with unanswered questions.

When Barbie enlists his father's help to reach out to Julia, he realizes that Don may know more about the Dome than he is letting on. Meanwhile, Big Jim appoints himself sheriff of Chester's Mill.

When Barbie is apprehended by a group of mysterious men, he is relentlessly interrogated about his connection to the Dome. Meanwhile, Big Jim makes a deal that could seal the fate of the residents of Chester’s Mill forever.

Big Jim finally learns the shocking truth about what really happened to his wife, Pauline, when they are reunited. Meanwhile, climate change poses a new threat to Chester’s Mill.

When temperatures begin to plunge, Sam and Rebecca spring into action to try to save the residents of Chester’s Mill. Meanwhile, Barbie risks his own life in order to save Julia after a terrible accident.

When a new threat from the Dome intensifies, the residents of Chester’s Mill find themselves at risk of being crushed to death. Meanwhile, Melanie’s health continues to deteriorate as the fate of the egg remains unknown.

Just as the walls start to close in on those trapped in Chester's Mill, a possible exit from the dome is revealed.