“I tried to write a book that would keep the pedal consistently to the metal,” Stephen King writes in an afterword to Under the Dome, his massive new novel — his 48th! — an explanation for why you will carry this heavy, bulky book everywhere, eager to gobble up a few more pages whenever you can. The novel is a monster, but it moves like a short story, devoid of the bloat and wordiness that has plagued the beloved author’s latter-period work.

King started toying with the book — about a small New England town named Chester’s Mill that suddenly becomes trapped beneath an invisible, impenetrable, inexplicable dome — in 1976, and many faint traces of The Stand course throughout. He picked up the premise again in the ‘80s, setting it inside an apartment building under the tantalizing title The Cannibals, but that attempt also fizzled.

By the time King finally licked Under the Dome, The Simpsons Movie had beat him to the idea of a town trapped under unbreakable glass. But no one in Springfield had their hands cut off by the dome’s sudden descent or crashed a plane into it or drove his car full speed into it or had the pacemaker in his chest explode when he got too close (the dome emits a mysterious, low-frequency electrical charge).

Moreover, no one in The Simpsons Movie was so cunning and manipulative as Chester’s Mill’s second selectman (and used-car salesman) Jim Rennie, who, with the help of his brutish (and increasingly murderous) son Junior, seizes on the fear and befuddlement that greet the dome’s appearance. Rennie swiftly takes control of the town and unofficially crowns himself king of his new fiefdom, in which no one — not the military, not CNN, not even President Obama — can interfere.

Under the Dome was written in a relatively scant 15 months, and the speed shows: Huge chunks of the book consist largely of dialogue, as if King was already thinking about a screenplay (miniseries talks are underway with HBO). But King’s ability to juggle a huge cast of characters and invest each with a distinct voice and personality has rarely been better, swooping with equal ease from the minds of a short-order cook, a May-December couple, a crazed meth addict, a chicken farmer, even a resourceful Corgi.

When writing about Samantha Bushey, the single mother of an infant boy and occasional drug abuser who lives in a trailer, King deftly captures her essence in just a couple of sentences. “She’d given up on the child-restraint seat months ago. Too much of a pain in the ass. And besides, she was a very safe driver.”

Unlike most of King’s epic-sized tales, the horrors in Under the Dome are all human (there are a couple of brief, vague instances of the supernatural and only a little bit involves aliens). The first murder occurs on Page 25, and many others follow.

Playing to one of his key strengths — his knack for crafting intricate plots in which unrelated characters inadvertently affect each other’s destinies — King turns Under the Dome into an exploration of the darkness that lurks beneath many a man’s heart, a darkness held in check only by the demands of civilized society. Remove its rules (“Get it through your head: “this town has receded”), and people’s instincts for self-preservation spring forth unchecked.

For those who are insane or harbor evil desires, the dome is an excuse to let their worst pour out. Not even The Stand had so many major characters come to gruesome ends.

The origins of the dome and its eventual resolution are dwelt with but only sparingly, and they are the book’s least interesting aspect. Although not quite so disappointing as the deus ex machina of The Stand (the hand of God) or the climactic revelation of the monstrous entity of It (a giant spider), the end of Under the Dome still seems limp: The last 100 pages are its weakest.

But everything that has preceded that finale is so utterly engrossing and awesomely entertaining, the let-down ending isn’t much of a problem. Under the Dome is the sort of book for which the phrase “page-turner” was coined: You’ll never tear through a 1,000-page book so fast.

Although King weaves contemporary themes — the Iraq War, Al Qaeda, global warming, terrorism — the book’s main hook is the same one that has earned him unparalleled success: He understands people and the horrible things they are capable of, but he also believes in the essential goodness of mankind.