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.

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.

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.