A steady, largely effective adaptation of the 2022 novel by A.M. Shine, writer-director Ishana Night Shyamalan’s “The Watchers” stars Dakota Fanning as an American working in a pet shop in Galway, Ireland, vaping her current life away.

A long-distance parrot delivery takes her (and parrot) to the Connemara region in western Ireland, through a scenic, oddly unmapped patch of forest where the Watchers reside. These creatures, barely glimpsed at first, move quickly, are prone to unsettling shrieks and, as the film proceeds, require more and more expository interludes for the four humans trapped in those woods. For now, they’re protected by a sleek concrete and glass bunker. Fanning’s character, Mina, is the fourth and latest visitor/prisoner, and the most determined to scoot.

The script follows the book’s story beats quite faithfully. The leader of the human survivors, Madeline (snow-haired Olwen Fouéré, whose unblinking intensity makes every utterance stick), has been trapped in the magical forest — magical in a not-fun way — the longest. Ciara, whose husband has gone missing-presumed-dead in the woods, is played by Georgina Campbell (also good, though the role feels thin). Twitchy, slightly off Daniel (Oliver Finnegan) makes the best of things and follows all the rules for survival, dutifully.

The Watchers come out of their subterranean tunnels when the sun sets, and (no spoilers here) appear to have a great interest in simply studying the humans behind the thick but not impenetrable windows of the bunker. How’d that bunker get there? What do these Watchers look like? What do they want? What past tragedy haunts Mina? As in the novel, the answers emerge in due course.

The most insinuating elements of this debut feature (Shyamalan’s filmmaker father, M. Night Shyamalan, served as one of the producers) point to a filmmaker of legitimate promise and a knack for slow builds. The movie isn’t gory (strike one in 2024) or innately sadistic (strike two). It’s also a little sludgy in the writing. There are times in “The Watchers” when Madeline, a sometime educator, we’re told, turns into a de facto adjunct professor specializing in expository restatement.

Time and the next feature will tell if Shyamalan can further develop her visual assurance while realizing not every story turn benefits from a verbal recap or footnote. Even with its drawbacks, I found “The Watchers” worth watching, even with its odd (and perhaps too faithful to the book) final 15 minutes. The director works well with cinematographer Eli Arenson to envelop the chamber-sized ensemble in various shades of dread, or comfort.

This tale of supernatural riddles wouldn’t work at all if we couldn’t invest in Mina’s psychic burden. Fanning doesn’t have to stress it; she knows how to let it come through in small matters of body language, and in the eyes. That makes acting sound easy, which it is not. Neither is adapting a story involving a dense underlay of folklore, in this case to imperfect but absorbing results. /Tribune News Service

“The Watchers” contains violence, terror and some thematic elements

“THE WATCHERS”

Rated PG-13. At the AMC Boston Common, South Bay Center Causeway, Alamo Drafthouse Seaport, Landmark Kendall Square Cinema and suburban theaters

Grade: B+