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.

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.