Barbie's life is in Big Jim's hands; the dome becomes magnetized; Julia tries to save the life of a mysterious girl who may have clues about the origin of the dome.

When Rebecca discovers an infestation of butterfly eggs on the crops, Barbie risks his life to help her save the town's food supply.

Big Jim conducts a census to see how long the town can survive on dwindling resources; acid rain threatens everyone.

Rebecca and Big Jim consider extreme measures as the conditions worsen in Chester's Mill; clues about Melanie's connection to the dome are revealed.

After Big Jim and Rebecca's plan left the town divided, Julia takes over as the leader of Chester's Mill; Norrie and Joe help Melanie find more clues.

As Barbie descends further into the mysterious tunnel in hope of finding Sam, he comes across a world filled with unanswered questions.

Barbie turns to his father for help contacting Julia but realizes that he may not be trustworthy; Big Jim declares himself sheriff of Chester's Mill.

Barbie is apprehended by mysterious men and relentlessly interrogated about the Dome; Big Jim forms a deal that could permanently seal the fate of the Chester's Mill residents.

Big Jim finally learns what happened to his wife, Pauline; Chester's Mill faces a new threat -- climate change.

Rebecca and Sam try to save Chester's Mill residents as temperatures plunge; Barbie puts his life at risk to help Julia after a terrible accident.

The latest threat intensifies, leaving Chester's Mill residents at risk of being crushed to death; Melanie's health declines as the egg's fate remains uncertain.

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