The very weirdness of Olivier Assayas’ second film with Kristen Stewart would seem to militate against it. “Personal Shopper” is set, to some extent at least, in the world of high fashion (Stewart plays Maureen Cartwright, a young American woman living in France, who picks out clothes and shoes for a rich woman too busy to do it herself). But it’s also a murder mystery of sorts, as well as a horror movie involving spectral phenomena that can apparently communicate with the living through modern devices like smart phones. It seems implausible that a combination of these elements should make for a successful film, but though its parts don’t entirely cohere, this is a fascinating, if sometimes frustrating, piece of work—a slow-moving, macabre psychological thriller that, while implausible, casts an intoxicating spell.

Cartwright, you see, isn’t merely the shopper of the title. She might also have psychic powers, which she is putting to the test by staying overnight in a house that’s supposedly haunted. (Apparently a couple considering buying the place won’t commit until they’re assured that any malignant spirits have been exorcised.) And that’s not all: the place was previously the home of her late twin brother Lewis and his girlfriend Lara (Sigrid Bouaziz), who’s trying to sell it. She shared a heart condition with Lewis, and years ago they had promised one another that whichever of them died first would attempt to contact the other from beyond. During her night in the house Maureen does encounter a ghost—a frightening apparition that sends her fleeing out the door. But it was not, she insists, Lewis.

On the job side, Cartwright continues to purchase wardrobe items for her employer Kyra (Nora von Waldstatten), whose celebrity status goes undefined but whose present lover, a journalist named Ingo (Lars Eidinger), offhandedly remarks that he thinks Kyra is about to dump him. Maureen must be careful, too, since the most important rule of her job is that she must never try on the garments she buys for Kyra; she does, though, first at the urging of some of the sellers, and then back at her apartment, where wearing the items gives her the vicarious thrill of being someone else.

A plot, of a sort, emerges when Maureen takes the channel train to England and begins receiving strange text messages suggesting that she’s being followed. The insistent texts have an erotic, threatening tone, and continue when she returns to Paris, setting up an assignation in a hotel room. Are the messages from Lewis? They’re certainly not from her boyfriend Gary (Ty Olwin), who’s off in Oman working on a long-term tech project and stays in touch only via Skype. Then a murder intervenes, and though the identity of the victim and how the search for the perpetrator progresses won’t be revealed here, it can be said that the picture offers a startling conclusion, though one that might provoke more questions than it answers.

Much about “Personal Shopper,” in fact, is befuddling, and it takes off on tangents that allow Assayas to indulge his filmmaking whims without really seeming to go anywhere. At one point, for example, Maureen consults an old Hammer-style movie about the psychic interests of novelist Victor Hugo, who conducted histrionic séances involving table-tapping spirits whose messages had to be worked out in transcription. The digression is just that, but Assayas seems to take enormous pleasure in recreating the sixties look of the clip, and that’s enough to justify its existence. There’s also a lovely scene involving some sort of presence moving unseen through a hotel lobby that’s carried off with a ridiculous simplicity that would have made James Whale proud; the fact that it doesn’t appear to have much connection to the plot is beside the point.

Much of the brooding mood of the picture, moreover, comes not from the director but his star. Stewart, with her hollowed-out look and her often blank expression, becomes a study in sorrow, obviously grief-stricken over Lewis’ death and desperately seeking some kind of closure while fearing what that might bring. Everybody else in the cast is purely functional, but the behind-the-camera contributions are essential to the atmosphere that Assayas and Stewart create—Yorick Le Saux’s dreamy camerawork, Francois-Renaud Labarthe’s production design, Marion Monnier’s halting editing, and especially Jurgen Doering’s costumes. Even the effects—absurdly rudimentary though they might be by Hollywood standards—seem entirely right.

You may come out of “Personal Shopper” scratching your head, but you will find it hard to shake off its effect.