What makes Kristen Stewart so arresting an actress is also what makes it so hard to describe what she does on screen. There’s something beguilingly mysterious about her that you can’t quite quantify. She’s there, but she’s also not there. It’s not that she’s bored or out of it, but rather that she seems to be operating on a strange frequency all her own. We watch Stewart in part because we can’t quite understand her.

That air of ambiguity is crucial to the strong spell that Personal Shopper weaves. I’ve seen this moody character study twice now, and I can’t say I’m any closer to unraveling its meanings or determining precisely why Stewart is so terrific in it. All I know is I want to watch it—and her—again very soon.

Written and directed by Olivier Assayas, who previously collaborated with Stewart on the comparably opaque Clouds of Sils Maria, Personal Shopper takes us into the world of Maureen (Stewart), who works in Paris as a personal assistant to a supermodel named Kyra. We rarely see Kyra, and Maureen’s life is one of isolation. In addition to an absent boss making demands from afar, she has a far-flung boyfriend who she occasionally chats with on Skype. But the greatest void comes from the recent death of her twin brother Lewis, who succumbed to a heart condition that she shares. Lewis was a medium, and Maureen is convinced that he will make contact with her from the great beyond. She spends her nights camped out at his home, waiting for him.

Personal Shopper is ostensibly a film about grief, but Assayas hasn’t plotted out a familiar trajectory for Maureen. For one thing, the movie sits intriguingly between genres: At any point in Personal Shopper, you may be watching a ghost story, a psychological thriller, a stalker drama, or a twisted love story. Assayas insists they can coexist, and likewise Stewart refuses to define exactly who Maureen is. We sense the bereavement the character is feeling, but Maureen is prickly and withdrawn, rarely expressing what she’s thinking. We watch her wondering what’s going on inside her, but the more we look, the less sure we are. 

This is Stewart’s great gift. In the five years since the end of the Twilight franchise, which exponentially raised her profile but also damaged her credibility among serious filmgoers, she has delivered a slew of terrific performances that have maximized her enigmatic quality. In movies as different as Still Alice, Clouds of Sils Maria, Cafe Society, and Certain Women, Stewart has played distant figures who, even when they’re front and center, seem to be just out of reach.

She’s never been so exposed as she is in Personal Shopper, but the disappearing act continues. Like a lot of people in the entertainment/fashion sphere, Maureen has learned that it’s best to withhold parts of herself so that they can’t be exploited. When she talks to people for her work, she’s direct and formal—partly because she doesn’t love her job and partly because she doesn’t want anyone close to her. (Even her Skype conversations with her boyfriend are a passionless back-and-forth.) But that distance is mitigated by what I can only describe as Stewart’s placidly edgy expression. It’s a look she wields in many of her performances, suggesting that anxiety is being held at bay, just barely. And in Personal Shopper it conveys whole universes of sadness and uncertainty. Maureen is holding it together, but we worry that she might crack.

Lord knows she’s got reason to fall apart. Beyond coping with the death of her brother, Maureen discovers that there definitely is … something hanging out at Lewis’s house. Later, she begins receiving text messages from an unknown sender, who seems to be following her every movement and knows what she’s thinking. Is it Lewis? Is it just some random creep? At first, the texts feel incredibly intrusive, but Maureen begins engaging with her phantom pen pal, lowering her guard in a way she doesn’t elsewhere in Personal Shopper. Here, Assayas turns one of the most banal, least cinematic elements of modern life—texting—into something seductive, scary, and sexy. When the film segues from there to a shocking, unexpected murder, we’re already so prepared for the next hairpin turn that we feel fully comfortable in Assayas and Stewart’s hands. 

Plenty of actors enrapture us for a finite period of time. Eventually we get used to their tricks, and grow tired of what feels like shtick. It’s a natural progression, and it’ll happen with Stewart one day. But a film like Personal Shopper will remain to remind us how absorbing she once was. Just as her allure is inscrutable, so too is the movie’s, as it gradually comes to a resolution without ever officially arriving at anything so concrete. Personal Shopper won’t let you go—it’s powered by one ghost mourning another.   

Grade: A-

Grierson & Leitch write about the movies regularly for the New Republic and host a podcast on film, Grierson & Leitch. Follow them on Twitter @griersonleitch or visit their site griersonleitch.com.