A protective mother lives with her two sons in an isolated woodlands house to which they must remain tethered by ropes, in order to protect against an omnipresent evil that only she can see.

Splat Pack veteran Alexandre Aja tries his hand at family-in-peril horror along the lines of the Quiet Place franchise with Never Let Go. But mostly, the French director just succeeds in making us miss his entertainingly trashy swerves into B-movie pulp, with creature features built around ravenously bitey carnivorous fish (Piranha 3D) or giant Florida gators riled up by a hurricane and flood (Crawl). Whatever their strengths and weaknesses, those movies were fun popcorn entertainment with teeth. Fun is banished from Aja’s latest, which starts out mildly intriguing and chalks up a few bracing jump scares before running out of juice.

This amorphous evil apparently has so poisoned humanity that civilization is over, and only the warmth and love of a house built by the boys’ grandfather as a refuge for his fearful wife can keep them safe. We get a dose of this setup from Nolan in voiceover and then a bunch more from Momma in ominous dinnertime stories and warnings both patiently nurturing and enraged. There’s even a rhyming incantation they recite before venturing out and another for once they’re back inside, their hands touching the sacred wood. The premise is encumbered with a lot of convoluted lore that somehow never makes it more coherent.

One manifestation of evil that appears especially interested in Momma is a hillbilly in a housedress (Kathryn Kirkpatrick) who drools ink and has a tongue like a lizard — or like Gene Simmons in his Kiss heyday. The suspicion arises early on that she was once part of the family. Also circling the house at night while Momma sits in a rocker on the porch, sharpening her hunting knife, is the boys’ late father (William Catlett), who looks alive aside from the huge shotgun hole in his back.

Momma is so furious after a close call caused by the boys’ recklessness that she threatens them at knifepoint while making them repeat the rhyme for the 800th time. She also has a kind of purification ritual where she shuts one of them at a time in the cellar to imagine the darkness taking over their world and then will themselves to come back into the light.

The movie has started to fall apart by that point due to the vagueness and repetitiveness of its plotting, so it’s a welcome shot of craziness when Berry threatens to go full Piper Laurie in Carrie. Sadly, she stops short of that hellfire hysteria (at least for now), sticking to a low-boil witchy intensity and a dread that occupies Momma’s every waking moment. Still, a seed is planted, hinting that her maternal devotion may be more twisted than it seems.

Hunger, fear and desperation drive a wedge between the brothers when Nolan begins to doubt his mother’s dire warnings and plots to set out ropeless in search of food. Since Momma is the only one who ever sees the evil, they have always had to take her word for it. But Samuel believes her unquestioningly, begging Nolan not to put them all at risk.

In his last film, the claustrophobic Netflix sci-fi survival thriller Oxygen, Aja took a setup that could not have been more confined and kept the scenario taut and the suspense humming. He’s working on a larger canvas with Never Let Go, a three-character Southern Gothic chamber piece. But the movie starts slackening almost as soon as we digest all of Momma’s teachings.

The friction between the brothers is well-played by the two terrific young actors — Jenkins has shouldered more than his fair share of evil lately, after Lee Daniels’ inadvertently campy possession freakout, The Deliverance — and the makeup team does excellent work on all three members of the principal cast, hollowing out their eyes and cheeks as malnutrition takes its toll. But there’s only so much mileage the movie can get out of “Is Momma crazy or speaking the truth?” before it becomes monotonous.