Offering more slowly simmering menace and dread than haunted-house scares, “It” finds its shocks in the terrors of childhood and its heart in the way the seven kids here band together to face them.

This adaptation of Stephen King’s 1986 novel is set in the the heart of King country, in the creepily quiet town of Derry, Maine. One rainy October day in 1988, little Georgie Denbrough (Jackson Robert Scott) takes a paper boat — lovingly made by his older brother, Bill (Jaeden Lieberher), in bed with a cold — out to float in the gutter. The boat falls into a storm drain, where it’s recovered by a strange figure: a scary-looking clown who calls himself Pennywise (played by Bill Skarsgard). The clown lures Georgie into the sewer, never to be seen again.

Months pass, and the town tries to forget about Georgie, as well as the other kids who mysteriously have gone missing since. But Bill and his buddies — hypochondriac Eddie (Jack Dylan Grazer), wise-cracking Richie (Finn Wolfhard) and reserved Stan (Wyatt Oleff) — haven’t forgotten. Their thoughts are preoccupied by the school bully, Henry Bowers (Nicholas Hamilton), and his bruiser buddies.

As their eighth-grade school year ends, Bill encourages his friends to spend the summer investigating Derry’s sewers in hopes of finding a clue to Georgie’s whereabouts. When they do, each of the boys sees something that terrifies him to his core — and, with each viewing, Pennywise also works his way into the picture.

The foursome soon adds members, bonding as targets of Henry’s wrath. There’s Ben (Jeremy Ray Taylor), the portly new kid, and Mike (Chosen Jacobs), a home-schooled kid who’s on Henry’s list apparently because he’s black. Then there’s Beverly (Sophia Lillis), who’s rumored to be promiscuous. They, too, have seen things they can’t explain.

These seven, who call themselves the Losers’ Club, compare notes and realize there’s something sinister in Derry’s history that rears its head every 27 years, feeding on children and their fears. This same evil has an effect on the adults, rendering them at best oblivious to the spreading terror and at worst abusive and threatening to their children. Beverly, living with her possessive father (Stephen Bogaert), suffers the worst on this front.

Director Andy Muschietti (“Mama”) and screenwriters Chase Palmer and Cary Fukunaga, with a polish by “Annabelle” writer Gary Dauberman, take their time getting to the core of “It” — the way Pennywise morphs to fit the fears of each kid, and how the kids learn to fight back when nobody else will. The horror is played thoughtfully, aiming more at being disturbing than jump-in-your-seat scary.

Muschietti also understands that “It,” a dense and complicated novel written at the height of the author‘s popularity, is the wellspring of all things Stephen King. Muschietti works in images familiar to watchers of other King adaptations — a shower of blood reminiscent of Sissy Spacek’s in “Carrie,” a character fashioned after Kathy Bates’ mad caregiver in “Misery,” the echoes of “Stand by Me” in the boys’ childhood banter — but they fold seamlessly into the whole, unlike the obvious Easter eggs planted in “The Dark Tower” to keep King fans from falling asleep.

Since the adult characters are nearly as inconsequential as the grown-ups in “Peanuts,” the movie rises and falls on the strength of its young ensemble. The seven are consistently good, with solid chemistry and a natural way with sarcastic banter. Only Lieberher, whose résumé includes the eerie “Midnight Special” and the off-track “Book of Henry,” and Wolfhard (”Stranger Things”) are familiar faces, and Lieberher is a strong anchor for the team. The find is Lillis as the Losers’ Club’s only girl, who not only holds her own against the boys but brings an added air of tragedy.

Fans of King’s book, or the much-loved 1990 miniseries, will note that this adaptation of “It” is missing half its weight, the part where the Losers’ Club reunites as adults. There’s talk of a sequel that would tell the rest of the story, but for now “It” is enough to make viewers’ skin crawl.

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’It’

Stephen King’s blockbuster novel about 13-year-olds who find a terrifying evil in their small town gets an adaptation that’s unsettling and creepy.

Where • Theaters everywhere.

When • Opens Friday, Sept. 8.

Rating • R for violence/horror, bloody images and language.

Running time • 135 minutes.