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.

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.