How distraught is Annette, the severely troubled British mother of two played by Daisy Ridley in “Magpie?” She has gotten a short angular haircut, one that might, in another context, be the height of chic (very Isabella Rossellini). Except that the movie uses it as a symbolic expression of her trauma, like Mia Farrow’s iconic Vidal Sassoon cut in “Rosemary’s Baby.” Annette, who’s on some serious medication, looks at a mirror until it breaks. Does she have telekinetic powers? No, she broke it with her hand (which bleeds into the sink), but the force of her repressed rage is palpable. Ben (Shazad Latif), her British Indian husband, is a noted author, and every comment she makes about his work is a sly dig. She speaks in brief, clipped “civilized” phrases. At one point a bird crashes into the window of her home. The whole atmosphere of the film is drenched in her cold anger.

Annette is suffering from something profound, but it’s not an illness. It’s the blues that can overwhelm mothers who are raising young children and feel alone, isolated, maybe abandoned. Ben, it turns out, committed a primal sin, and it was simply this: After their son, Lucas, was born, he went away for months to research a book, with no awareness of how much Annette needed him. He put all the responsibility on her, and when he returned, she was never the same.

The complex and even traumatized undercurrent that some mothers experience isn’t merely a good subject for a movie; it’s one that’s long overdue. Yet “Magpie” presents Annette to the audience in a way that seems rather extreme, and the entire movie is like that. Most of us don’t blink an eye at cinematic real-estate porn, but the house that Annette and Ben have in the country outside London is as huge and roomy as a museum. When Annette goes to lunch with a former colleague, the stiltedness of their connection — and the sound of Lucas crying in the restaurant — infuses every moment with awkwardness. And then the plot kicks in. Annette and Ben’s daughter, Matilda (Hiba Ahmed), who’s around eight, has been cast in a big-budget costume drama, where she’s set to play the daughter of the main character, who’s being portrayed by a glamorous Italian movie star named Alicia (Matilda Lutz).

Ben is chaperoning Matilda on set, and we’re cued, from minute one, to see that he and Alicia have a connection (a lot more of one than he seems to have with his wife). In case we miss the point, a tabloid website runs a paparazzi shot of the two them, asking who Alicia’s new “mystery man” is…and it’s only the second day of the shoot. Much of “Magpie” feels overstated yet underwritten. It’s fine that the film shows us Ben’s interest piqued by a celebrity sex tape of Alicia. But does it have to underline the point by having him masturbate to it in the shower, and having Annette hear him through the door? As Ben and Alicia develop a mutual crush, the atmosphere the film seems to be going for is gloomy indie “Fatal Attraction.” And my thought was: “Fatal Attraction” was a lot subtler.

As “Magpie” goes on, though, a funny thing happens. You begin to settle into the film’s overly telegraphed style, its mixture of obviousness and enigma. You accept that this is not Hitchcock, or even Adrian Lyne. The first-time director, Sam Yates, working from a utilitarian script by Tom Bateman, slathers on mood, yet there’s a primitive charge to the film’s no-frills staging. You want to see what’s going to happen next. And Daisy Ridley, whose idea the movie was based on, knows exactly what she’s doing. She dares to play Annette as brittle and “unreasonable,” because that’s just how a man like Ben would view her. He doesn’t realize that he’s the problem: his entitlement, his cluelessness about what mothers actually go through. He just wants to leave it all behind and plunge into an affair with Alicia, whose attentions are so flattering. The two begin to text, flirtatiously and then ardently. He thinks that he’s found a way out of his doldrums. But he has no idea what’s really happening. And neither does the audience.

Shazad Latif, with his tall handsomeness, his gentle grin, and his man-bun, plays Ben as someone who has worked hard to be sensitive, and therefore thinks that what he wants he deserves. But he’s deluded. He is, on the film’s own terms, toxic, but “Magpie” isn’t a harangue. It’s a thriller, and for all the Screenwriting 101 simplicity of many of its scenes, it builds toward a climax that’s disarmingly fun and satisfying. It’s one of those “Usual Suspects”/”Saltburn” twists, which means you have to accept that there’s a certain only-in-the-movies logic to it. But when the twist arrives, it has a crowd-pleasing resonance. It’s not just about playing games. It’s about a mother saying how much she wants to be loved.