A peaceful day in the small Maine town of Chester's Mill turns into a nightmare when an invisible, impenetrable dome slams down around the town, trapping the townspeople and several passing strangers inside.
When Paul escapes from custody, Big Jim worries that Linda can't handle it so he organizes a search party and takes Barbie along. Meanwhile, Joe finds his house the center of attention when the teenagers realize he has a generator and no parents at home, and Junior tries to find a way out beneath the dome.
A meningitis epidemic breaks out in Chester's Mill and Barbie and Big Jim track down the individual who has stolen the antibiotic they need to treat the disease. Meanwhile, Norrie and Joe try to determine the cause of their seizures, and Julia discovers the secret her husband Peter was hiding from her.
The government busses visitors in to communicate with their loved ones trapped within the Dome. Meanwhile, Barbie learns from a soldier that the Army plans to drop a bomb on the Dome when it threatens the outside world.
Joe and Norrie try to track the source of the dome and find an amazing discovery. Meanwhile, the dome seemingly induces labor in a woman, forcing Alice and Barbie to help deliver the child. And Big Jim discovers that his control of the town is threatened.
Ollie tries to wrest control of Chester's Mill from Big Jim, who launches an attack on the farmer's well. Meanwhile, Joe shows Julia the black egg, and Norrie comes to terms with her mother's death.
After she has a seizure, Junior shows Angie a painting his mother made that sheds some light on the secrets of the Dome. While Joe and Norrie try to find the missing mini-dome, Big Jim receives a visitor from a past and organizes a voluntary program to collect guns from the townspeople.
Maxine continues to tighten her grip on Chester's Mill with Barbie's unwilling help, so he decides to tell Julia the truth about her husband's death. Meanwhile, Big Jim finds out why Maxine is so interested in Chester's Mill, and Joe, Norrie, and Angie find the fourth hand.
There's no fury like a woman scorned when Maxine takes revenge for Barbie rejecting her. Meanwhile, Angie, Joe, Junior, and Norrie grow closer to learning the secret of the Dome. However, when one of them leaves the circle, the Dome makes its displeasure clear.
As darkness settles on Chester's Mill, the Dome finally speaks to the group, but its answers prove less than helpful. The Monarch is revealed, and Big Jim tightens his grip on the town and his son.