Director William Brent Bell, who showed an unusual concern for stable camerawork in the otherwise dreary found-footage exorcism opus “The Devil Inside,” again demonstrates solid competence in classical filmmaking technique with “The Boy.” Unfortunately, the silly script by Stacey Menear undermines both Bell’s rather elegant work (along with that of his behind-the-scenes collaborators, production designer John Willett, art director James Steuart and cinematographer Daniel Pearl) and the committed efforts of his stars Lauren Cohan and Rupert Evans. The result is a feature-length version of what might once have been a middle-grade episode of Rod Serling’s “Night Gallery,” or going even further back, of “Thriller” with Boris Karloff.

Cohan plays Greta, a young American who, in order to get as far away as possible from her abusive boyfriend Cole (Ben Robson), takes a job as nanny to an eight-year old boy at a remote British manor house. After she arrives at the place, which looks from the outside like a fairytale castle, however, she gets a shock when the surprisingly elderly Mr. and Mrs. Heelshire (genially dotty Jim Norton and haughtily hard-boiled Diana Hardcastle) introduce her to their son Brahms. The boy turns out to be a life-sized porcelain doll that Greta is expected to treat as if it were alive, following a set of rules about waking him, dressing him, putting him to bed (with a goodnight kiss), playing him music and reading to him regularly. She’s barely had time to settle in before the Heelshires go off on a vacation that, it turns out, will be longer than originally expected.

Initially unnerved and somewhat amused by her assignment, Greta nonetheless follows instructions, for the most part at least; and she develops a bond with the Heelshire’s cheeky deliveryman Malcolm (the likable Evans), who’s obviously interested in persuading her that nothing really prevents her from leaving the house (otherwise a no-no) for a night out with him. He also provides some revealing details about the late Brahms’ mischievous—or malicious—nature, his death in a fire two decades earlier, an unfortunate neighbor girl who was his playmate, and his parents’ adoption of the doll as a surrogate to assuage their grief after his demise.

All of that is in the background when odd things start happening in the house, especially when Greta fails to follow the rules to the letter. There are the usual bumps in the night, creaking doors and what sound like footfalls. Lights flicker. On the night she’s to go out with Malcolm, noises lure Greta up into the attic, and the spring-controlled stairs snap shut behind her, locking her in. The doll appears to move by itself. A sandwich is even left at the door of her room at one point. No wonder Greta begins to believe that Brahms’ ghost is haunting the place, using the doll as its instrument, and Cohan moves convincingly from amiability to subdued fear as concern sets in.

Matters come to a head when brutish Cole shows up, demanding that Greta go back to America with him. He’s derisive about the arrangement she’s fallen into, and contemptuous toward the notion that the doll is possessed by some evil spirit. Malcolm interrupts the confrontation, but it’s Cole’s presence—and the threat he poses to the stability the Heelshires had tried to establish—that reveals what’s really going on at the manor. Unfortunately, that revelation turns out to be a dreary horror trope that results in a lot of silly action before a goofy epilogue.

For the first hour or so, “The Boy” is a fairly effective slow-burning chiller, old-fashioned and silly but nicely crafted, with Brian Berdan’s editing and Bear McCreary’s understated score contributing to the atmosphere. In the final third, however, it collapses into preposterous cliché, and even technically grows ragged and scraggly down the home stretch. Forty years ago or so—when ABC could air one of its scary movies of the week like “Bad Ronald” (hint, hint)—it might have passed muster; now it comes across like a well-preserved genre antique.