In Chester's Mill, Maine, a strange occurrence locks the town in under an invisible dome-like surface.

Following Duke's death, his house catches fire, forcing the town to rally together to form a bucket brigade. Elsewhere, Junior ambushes Barbie, while Dodee and Phil pick up a military frequency.

After a Deputy is killed, Big Jim organizes a search party to hunt down the culprit. Meanwhile, Joe and Norrie continue to experience strange seizures.

The town suffers from an outbreak of meningitis. Julia learns that Phil and Barbie are connected to her missing husband. Angie struggles to escape the bomb shelter.

When friends and family from outside the dome come to visit, Barbie learns the military plan to destroy the dome with a missile.

After Julia and Dodee speculate that the source of the radio signal jam could be the answer to the dome's origin, they are led to Joe and Norrie. Meanwhile, Angie seeks help after escaping from Junior.

A friend of Julia's goes into labour after touching the dome. Big Jim kicks out Junior. Linda seeks out the Dundee brothers after Rose's murder. Joe and Norrie find a second mini-dome that holds a mysterious egg inside it.

Norrie grieves over her mom's death. Joe shows Julia the mini-dome. Big Jim makes a plan of action when Ollie takes control of food and water.

Julia takes Barbie to see the mini-dome and the egg, but they have both disappeared. A former acquaintance of Big Jim and Barbie makes a re-appearance. Angie starts to experience the same seizures as Joe and Norrie.

Maxine continues to manipulate Barbie and Big Jim. Linda and Julia investigate Duke's involvement with previous criminal activity in Chester's Mill. Meanwhile, Angie realizes Junior is the "fourth hand".

After Junior abandons Angie, Joe and Norrie, the weather turns nasty. Julia is shot by Maxine. Big Jim convinces Linda his stash of propane is what's saving the town and the biggest threat they face is from Barbie.

Big Jim rallies the town against Barbie after framing him for the murders and the shooting of Julia. Joe and Norrie move the mini-dome to Ben's house but it soon begins to act strangely.

As Barbie's fate is sealed by Big Jim, the dome blackens and the identity of the Monarch is revealed.