There have been many silly horror movies and psychological thrillers lately, but it’s difficult to think of one quite as dumb as “Shut In,” which recalls nothing more than one of the terrible movies-of-the-week that ABC used to broadcast in the seventies. Astonishingly, Christina Hodson’s script made the so-called Black List in 2012, which makes one wonder about the value of that annual compilation of unproduced screenplays with supposed promise.

Naomi Watts has the unenviable task of trying to make something of the role of Mary Portman, a clinical psychologist who has a practice—apparently specializing in troubled children—in a building next to her isolated home in rustic Maine. In a prologue we are shown a terrible car accident that takes the life of her husband as he’s driving his son Steven (Charlie Heaton)—Mary’s stepson, who has recently been expelled from school for problem behavior—to some sort of boarding school. Steven survives the accident, but in a persistent vegetative state.

Six months later (why is it always six in these stories?), Mary is caring for the unresponsive Steven at home, but after conferring via Skype with her close friend and mentor Dr. Wilson (Oliver Platt), she is considering moving him to a live-in facility. At the same time she is treating young Tom (Jacob Tremblay), a mute orphan boy about to be transferred from the institution he’s living in because of his behavior. That night Tom shows up at the house, and Mary takes him in.

That’s when the problems start. Tom disappears, presumably having run into the woods. Mary begins having nightmares about him and hearing bumps in the night. Dr. Wilson suggests that she’s suffering from stress and imagining things, but the increasingly high-strung woman thinks otherwise. It would be unfair to reveal precisely what’s happening, but perhaps one might suspect Doug Hart (David Cubitt)—the father of another of Mary’s patients, young Aaron (Alex Braunstein)—who suddenly evinces a possible romantic interest in Mary, as being the culprit. Or perhaps he’s just a red herring.

Suffice it to say that the big twist, when it does come, is so utterly ludicrous that it’s hard to take it seriously. It necessitates a hilariously over-the-top turn from one of players, whose scenery-chewing grows more and more ravenous over the course of the final half-hour, which is spent watching the villain skulking about the house with axe in hand (and nailing all the windows shut to prevent escape) while the potential victims try to remain hidden in closets. The sequence goes on much too long, with the baddie being repeatedly knocked out, only to revive at the worst possible moment, and an intervention by an outside party that comes off as a bad imitation of a comparable scene in “The Shining.” A body shows up at one point in an archetypal “gotcha” moment, but it’s not even clear whose it is.

You have to give Watts credit for investing so fully in a role that, as written, frankly suggests that the character is simply dense rather than a psychotherapist who should ever be trusted with the treatment of one child, let alone a whole troupe of them, especially since she seems to just leave Steven sitting in his wheelchair for hours on end with nothing but the TV for company while she goes about her daily routine. Tremblay, who was so remarkable in “Room,” is little more than a moppet prop here, while the up-and-coming Heaton might consider looking for a new agent. Platt, meanwhile, plays yet another avuncular psychiatrist, a role that’s becoming all too familiar to him (see “The 9th Life of Louis Drax”). Given the quality of the material, Yves Belanger’s cinematography is actually pretty good, though neither he nor director Farren Blackburn manages to clarify the layout of the house in which the action occurs. Nathaniel Mechaly’s score tries desperately to ratchet up tension, to little effect.

“Shut In” won’t scare you, except with its awfulness, but if you need a good laugh it might do the trick.