An invisible and mysterious force field descends upon a small fictional town of Chester's Mill, Maine, USA, trapping residents inside, cut off from the rest of civilization. The trapped townsfolk must discover the secrets and purpose of the "dome" and its origins, while coming to learn more than they ever knew about each other.

Julia Shumway: [Opening narration, season 1] Chester's Mill is a place like any other. At least, it used to be until we were cut off from the rest of the world by a mysterious dome. Invisible, indestructible, and completely inescapable. We're trapped. We don't know where it came from or why it's here, but now that we're all trapped under the dome together, none of our secrets are safe.
Dale 'Barbie' Barbara: [Opening narration, season 2] Two weeks ago, an invisible dome crashed down on Chester's Mill, cutting us off from the rest of the world. Why the dome is here or what mysteries lie ahead, we still don't know. Every day it tests our limits, bringing out the best and the worst in us. Some say we'll be stuck here forever, but we will never stop fighting to find a way out.
Joe McAlister, Norrie Calvert-Hill: The pink stars are falling. The pink stars are falling in lines.
James 'Big Jim' Rennie: [Opening Narration, Season 3] Four weeks ago, an invisible dome crashed down on Chester's Mill, cutting us off from the rest of the world. The dome has tested our limits, forcing each of us to confront our own personal demons... rage... grief... fear. Now, in order to survive, we must battle our most dangerous adversary... the enemy within.