As the Dome in Chester's Mill comes down, The Resistance, led by Barbie, Julia and Big Jim, makes a final attempt to protect the outside world from the infected townspeople in The Kinship, including Sam and Junior, and their new queen, Dawn.

When the Dome's calcification process accelerates, Chester's Mill has 24 hours before the barrier's breakdown will suffocate everyone inside. While the new deadline puts added pressure on Joe to bring the Dome down, Barbie and Julia race to save his child from The Kinship.

Members of The Resistance race to release their loved ones from Christine's influence before she reaches her end game for the Dome. While Barbie risks everything in an attempt to free Eva from the Kinship, Big Jim and Julia are enlisted by Hektor, the head of Aktaion, to test a possible cure for infected townspeople.

The Resistance, the citizen not under Christine's control, join forces with an unexpected ally: Hektor Martin, the nefarious head of Aktaion. Despite Hektor revealing more about the Dome's origins and helping to strike back at it, Big Jim and Julia still worry he will betray them. Meanwhile, Hunter receives encrypted files that give disturbing insights into the final effect the Dome will have on the infected townspeople.

Big Jim and Julia devise plans to end Christine's control over the town by initiating a life-or-death plot involving Barbie and Eva, while Joe and Norrie conduct research to better understand the Dome's ultimate agenda. Meanwhile, Hunter finds more information about the true head of Aktaion, the nefarious private corporation that wants to harness the Dome's energy.

Big Jim, Julia, Joe, Norrie and Hunter join together to form a resistance against Christine, who is mobilizing residents to work on a massive excavation project in the caves underneath the town. Also, Hunter uses his tech skills to contact the outside world.

As the world outside the Dome is rocked by a catastrophic meteor shower, unexpected alliances form inside the barrier. Eva tries to indoctrinate Barbie deeper into The Kinship and Big Jim and Julia turn to one another while isolated on Bird Island outside of town. Also, Joe is forced to accept help from Sam, the man who killed his sister.

For information about her agenda. Also, when Joe and Norrie question the town's new rules, they find themselves in a dangerous face-off with the increasingly unstable residents.

Big Jim and Julia form a tentative alliance to search for proof that will discredit Christine, which leads them to new information about the Dome's capabilities. Meanwhile, when tensions run high in town and threaten Christine's leadership, she puts a plan in play that has deadly consequences.

Under the guise of helping Chester's Mill rebuild, Christine urges the townspeople towards specific individuals and projects that remind them of their experience in the tunnels. Also, Julia and Big Jim make shocking discoveries that reveal a new threat within the Dome.

The residents of Chester's Mill try to move on with their lives in the aftermath of their mysterious experience in the tunnels beneath town. Meanwhile, Big Jim suspects new residents Christine and Eva are keeping secrets concerning the Dome.

Chester's Mill residents appear inside and outside the Dome following an exit into the tunnels beneath the town. Meanwhile, the Dome begins to reveal its ultimate agenda; and surprising alliances form as new residents emerge.

Season 3 begins with Chester's Mill residents appearing inside and outside the Dome following an evacuation into the tunnels beneath the town. Meanwhile, the Dome begins to reveal its ultimate agenda; and surprising alliances form as new residents emerge.