I so loved Olivier Assayas’s last film, his entrancing ponder of art and age, Clouds of Sils Maria, that his newest work, Personal Shopper, was probably my most anticipated film at the Cannes Film Festival this year. (It premieres here on Tuesday.) It’s got Kristen Stewart, who asserted herself as a natural, thinking actor in Sils Maria, and, on paper, it’s got a hooky, sexy, glam premise: Stewart plays, well, a personal shopper for a celebrity living in Paris, and there’s a ghost involved. So, expectations were high, but nothing in the plot description could have prepared me for Personal Shopper, which is strange, frightening, and possessed of a dark ribbon of sadness that no champagne gulped down at a post-screening beach party could drown out. Though the film has received a mixed reception here in France, Personal Shopper is the most arresting festival entry I’ve seen this year.

I’m going to get, well, personal for a moment, if you’ll indulge me. When I was 28, one of my very best friends, also 28, dropped dead of a heart attack. She was in Los Angeles, far away from where I was, and her very shocking death—though she had a congenital heart condition, doctors assured her it would not be a problem until well into middle age—sent me reeling in ways that I didn’t expect.

There was the crying and the missing and the awful bleakness of her funeral, of course. But the suddenness of it all, her young body failing her in one terrible judder, sent me into a years long cycle of anxiety and fear. A dormant tendency for panic attacks flared up again, stoked on by a constant, murmuring hypochondria. I made myriad doctor’s appointments, convinced I was about to have a stroke or an embolism. I frequently had to rush out of subway cars and movie screenings (sorry, The Bling Ring; I’ve still never seen you in full). I was overcome by mounting swells of dread, ones I’ve only now, four years later, finally gotten under some sense of control.

In short, the death of my friend—quick and cruel as it was—scared the hell out of me. And as selfish as that may be, to be so concerned for my own dumb life when my friend’s recently ended so tragically and unceremoniously, it was a huge, defining part of how I grieved for her. Death is scary. And we don’t always get to gently send people off into the unknown. Sometimes they’re sucked into it, while the rest of us aren’t looking. And when that person is young, when their death is so unplanned for, it has the uniquely jarring effect (at least in my experience) of making the world a terrifying, surreal place. How did no one tell us that it can be this easy to lose someone, and to die ourselves?

Which is why, when it’s revealed, pretty early on in Personal Shopper, that Stewart’s character, a bored gofer for a mean, charity-going socialite, had a twin brother with a congenital heart defect who died of a heart attack at age 27, Assayas’s film seemed to reach out to me directly, its silvery hands grasping at my head, heart, and throat. In its depiction of the horror of grief, the film is bracingly relatable, like some signal from out in the dark.

It’s a perplexing film. And I think I’m telling you about my own experience to clarify why Personal Shopper’s disorienting veers in plot and style—this is a horror movie with a matte, flat-faced demeanor, a grief drama with a shiver of sylphic humor—worked so well on me. Judging from the scattered boos and hisses at the Cannes press screening, Personal Shopper is not a movie whose ghostly ambiguity works on everyone. But, fan of Assayas and survivor of a vaguely similar experience (I didn’t lose a sibling, but still) as I am, I think Personal Shopper is as cathartic as it is terrifying, as knowing and wise about the weirder mechanics of the grieving process as it is utterly confusing.

I’ve not mentioned plot, mostly because I don’t want to. This film reveals itself in such beguiling, surprising ways that it really deserves fresh, unspoiled eyes. But I’ll tell you that Stewart’s character, the plainly named Maureen, lives in Paris and hopes to commune with the ghost of her dead brother. She spends some nights in a lonely, drafty house outside the city where he used to live, mournfully, timidly calling out to him, seeking some sign that he’s lingering there in the room with her. We also see Maureen going about the quotidian, but certainly glamorous, rituals of her job. She travels to London, she looks at great clothes (Chanel, as it did in Sils Maria, features prominently here), she rides her scooter around Paris with a determined blankness.

What are we to make of that title? Personal Shopper suggests something sprightly, a glossy David Frankel romantic comedy. Assayas’s film is certainly not that. I think it refers to the fact that Maureen is, in some ways, a ghost herself. Her client comes home to find things magically appeared, or moved around, resolved or settled. Like Maureen was never there. Except she was.

Stewart is not yet an actress of sprawling range, but what she’s able to do in this vein, not so much playing a character as expressively inhabiting a mood, is rather remarkable. Here is a pragmatic, emotionally muted, guarded young woman who is also immeasurably sad—a twin without her counterpart, a lone being who is, by the miracle of her birth, not supposed to be alone. Much of Personal Shopper is about aloneness, the lack of presence. There’s a line at the very end of the film that asks a fascinating, eternal question, wondering if the dead are alone in whatever next place they’re in, or if it’s us the living who have been left behind. Assayas’s film answers zero questions—it poses a million—but its deepest dips into the unknowable fathoms of existence could never yield answers anyway. Stewart plays this curious liminal energy—Maureen can channel into the spiritual plane, but is very much a citizen of the hard and practical real world—with a delicacy and a deep commitment. Her performance suggests she and Assayas are connected on some peculiar, powerful wavelength. She just gets him, somehow.

I think I get the film. Or, I get what Personal Shopper says to me. It’s a horror movie, and a downright terrifying one. There are certain scenes—scored by ominous thuds and whispering wind—that are so frightening that they were, for this wimp, extraordinarily hard to watch. But Maureen remains heartbreakingly resolute as she presses on into the most terrifying things: she needs to understand death, or at least confront it, before she can accept its grim, boggling premise. In its mixing of Sils Maria-esque unimpressed luxury (Stewart played an assistant in that one, too) with rattling, sometimes funny spookiness, Personal Shopper can be discordant. But there’s a reward at the end of all that tonal shifting.

Personal Shopper does not say anything easily comforting by the time its mysterious final scene has come to a close. The film is about, I think (though, honestly, who really knows), what’s pried open in the wake of death, a door newly ajar that calls out to us with both allure and menace. When my friend died, the strangest feeling I had was almost something like jealousy. Because she finally knew, she had an answer to life’s greatest gnawing question. Personal Shopper understands an odd, frightening duality. The not wanting to go—all the real, instinctual terror of not wanting to die—but still the persistent, needling voice of mourning, the one that says not, “Come back,” but asks, “Is it safe for me there, too?”