At 11:44 a.m. on October 21, the small Maine town of Chester's Mill is abruptly and gruesomely separated from the outside world by an invisible, semipermeable barrier of unknown origin.

The immediate appearance of the barrier causes a number of injuries and fatalities and traps former Army Captain Dale "Barbie" Barbara—who is trying to leave Chester's Mill because of a local dispute—inside the town.

Big Jim exerts a significant influence on Chester's Mill and seizes the opportunity to use the barrier as part of a power play to take over the town.

Junior has frequent migraines caused by an as-yet-undiscovered brain tumor which has begun affecting his mental state; unknown to Big Jim, Junior was in the process of beating and strangling a girl (Angie McCain) to death when the barrier appeared and has killed another girl (Dodee Sanders) by the time Big Jim places him on the police force.

Elsewhere in Chester's Mill, Col. James O. Cox (who is stationed outside of the Dome) calls Julia Shumway, the editor of the local newspaper, and has her carry a message to Barbie to contact him.

Around this time, Brenda Perkins, Duke's widow, discovers a file on her husband's computer that lists Big Jim's money-stealing schemes.

They conclude that the device was put in place by extraterrestrial "leatherheads" (so named for their appearance), and that specifically they are juveniles who have set up the Dome as a form of entertainment, a sort of ant farm used to capture sentient beings and allow their captors to view everything that happens to them.

On an organized "Visitors Day"—when people outside the Dome can meet at its edge with people within—Big Jim sends Randolph and a detachment of police to take back control of his former methamphetamine operation from Phil "Chef" Bushey, who is stopping Big Jim from covering up the operation as well as hoarding the more than four hundred tanks of propane stored there (Chef wants it all, explaining, "I need it to cook").

More than a thousand of the town's residents are incinerated on national television, leaving alive just over 300 individuals who gradually die out as the toxic air restricts their breathing.

The survivors at the barn begin to slowly asphyxiate, despite efforts by the Army to force clean air through the walls of the Dome using industrial-size fans.

The Dome rises slowly and vanishes, allowing the toxic air to dissipate and finally freeing what is left of the town of Chester's Mill.

[7] As King stated on his official site, these two unfinished works "were two very different attempts to utilize the same idea, which concerns itself with how people behave when they are cut off from the society they've always belonged to.

"[11]In an interview for PopEater.com, King admitted the book's environmental theme:[12] From the very beginning, I saw it as a chance to write about the serious ecological problems that we face in the world today.

We have this little blue world that we've all seen from outer space, and it appears like that's about all there is.In an interview with James Lileks of the Star Tribune, King said:[13] It's a natural allegorical situation, without whamming the reader over the head with it.

He wasn't actively evil, he was just incompetent—which is how I always felt about George W. Bush.Speaking to The New York Times Book Review, King said:[15] I enjoyed taking the Bush–Cheney dynamic and shrinking it to the small-town level.

On December 16, 2009, Stephen King held a book signing at the Magic Lantern movie theater in Bridgton, Maine, the town that the fictitious Chester's Mill is modeled after.

[24][25] A number of viral marketing websites for popular locations referenced in Under the Dome were created to publicize the book, including Big Jim Rennie's Used Cars, the Sweet Briar Rose Diner, the Chester's Mill Democrat Newspaper, and others.

These editions feature a dust jacket without any lettering, a removable band with author name and title, printed endpapers with the map of the town in color (regular edition contains a black and white map in the book's front matter), 27 illustrations by The New Yorker cartoonist Matthew Diffee, a ribbon marker, and also contain a deck of cards with the Diffee illustrations.

[26] A signed and numbered UK edition, published by Hodder & Stoughton, sold exclusively by both Hatchard's Bookshop and Waterstones, was limited to 500 copies.

[27] The author Dan Simmons, to whom Stephen King sent the manuscript for Under the Dome as a gift, commented on it on May 5, 2009, calling the novel "huge, generous, sprawling, infinitely energetic [...], absolutely enjoyable and impressive.

The review said the book contains "themes and images from King's earlier fiction, and while this novel doesn't have the moral weight of, say, The Stand, nevertheless, it's a nonstop thrill ride as well as a disturbing, moving meditation on our capacity for good and evil".

"[33] Ted Anthony of the Associated Press states that "Under the Dome is one of those works of fiction that manages to be both pulp and high art, that successfully—and very improbably—captures the national zeitgeist at this particularly strange and breathless period in American history.

"[35] James Parker of the New York Times noted in his review of Under the Dome that the novel contains lines that are "stinkers", which made him feel "the clutch of sorrow."

Regarding King's "pulp speed" output, James Parker noted: "We shouldn't be too squeamish about the odd half-baked simile or lapse into B-movie dialogue.

"[36] The review in the New York Post states that Under the Dome "shares some of The Stand's faults, like a left-field disaster [...] that works almost as a reverse deus ex machina, randomly wiping out half the cast.

"[37] John Dugdale, in a review for The Sunday Times wrote: "King's inability to raise his game—to relinquish the methods of his more straightforward tales of the paranormal—prevents you taking his socio-political vision seriously.

The simple division of characters into goodies and baddies, the use of magic, the homespun style, the sentimental ending, the vital role played by a dog in defeating the forces of evil—all of these belong in fiction for older children, not the grown-up novels he's bent on emulating.

"[38] Shortly after the release of the book, it was announced that Steven Spielberg's DreamWorks Television would be developing a cable miniseries based on the novel.