Any horror nut will tell you not to have sex without anticipating trouble, but what makes Arthur Harari’s The Unknown (L’Inconnu) so mesmerizingly unsettling is that calling this sui generis freakout horror or sci-fi or even fantasy seems simplistic. There’s a surface kinship here with films like It Follows and especially Under the Skin, in which post-coital afterglow sours fast. But the director declines to get too specific about his allegorical intent, which could be sexual trauma or gender identity or just a mysterious body-snatcher nightmare. Either way, this is a spellbinding psychological puzzler led by a typically fearless performance from Léa Seydoux.

Citing influences from Kafka to Antonioni, Harari has less interest in providing definitive answers to the film’s enigma than in exploring existential questions of metamorphosis, transformation, erasure and displacement. He could also be commenting on our growing disconnect from reality — social, political, cultural, spiritual, sexual — to the point where we no longer recognize ourselves. The kind of alienation the movie depicts seems entirely germane to the churning anxieties of our age of hyper-connectivity, as does nostalgia for simpler times in which self-reflection wasn’t quite so punishing.

The impulse for anyone who has consumed much science-fiction psychological horror will be to assume some kind of soul-sucking entity has gotten loose in contemporary Paris, using sex as a means of occupying new host bodies. But nothing is that straightforward or easily solved in The Unknown, as the title implies.

Based on the graphic novel The Case of David Zimmerman, by the director (the Oscar-winning co-screenwriter of Anatomy of a Fall) and his brother Lucas Harari, the film was scripted by them with Vincent Poymiro. It opens in the title character’s messy apartment in the outer Paris suburbs. David is played by Niels Schneider as a man haunted even before his life and identity are pulled out from under him, looking like a gaunt flamenco dancer gone to seed with his stringy black hair and goatee. 

While David appears never to have shown his work to a gallery or an art dealer or even to friends, he’s obsessive about photography. He collects monochromatic vintage postcards of Paris and roams around the city capturing images of how those same places look now. He might be called a documenter of ghost buildings in a city crawling with demolition and construction crews and sprouting high-rises. Again, erasure.

He would prefer to stay home alone, but two friends come knocking and David gets reluctantly dragged to a mega-party, a druggy hipster happening that’s part rave, part political protest, with giant puppet heads of authoritarian world leaders bobbing about among the crowd. And yes, there’s a “yuge” papier-mâché Trump head that gets pulped like a piñata.

David is one of the few people there not wearing a grotesque mask or crazy costume. He also seems the only one determined not to have a good time, so much so that a stranger passes him a pill, “to loosen you up.” Soon after, he locks eyes with a woman standing alone by an exit door (Léa Seydoux), in a kind of tunnel vision that drills right through the packed space. 

She gives a subtle nod for him to follow as she slips out down a stairwell. No sooner does he join her than she removes her underwear without a word and straddles him, grinding to a climax before falling backward unconscious. There’s no agony or ecstasy in their sexual congress, which seems almost animalistic, less driven by lust than by some indefinable compulsion.  

David leaves the scene and the woman, whose name we later find out is Eva Heisinger, staggers back upstairs and weaves her way to the door. She is helped into a cab, giving David’s address as her destination. Once inside his apartment, she gets a surprise — or rather, David does — when he/she looks in the mirror and realizes he’s in the body of the unknown woman. Seydoux plays the scene with a mix of alarm and queasy fascination, stripping down and going over every inch of her body like it’s an alien landscape.

Soon after, David, in Eva’s body, remembers seeing her waitressing at his parents’ 50th wedding anniversary party, which explains the blurry negative of her hanging in his darkroom before the body-swap happened. 

Dreams and reality collide, but when David’s body does resurface, he’s now host to a different woman, a 20-year-old named Malia (Lilith Grasmug) who was reported missing some time back. This yields a hint of sardonic humor as Malia grumbles about losing 20 years of her life now that she’s stuck in the body of David, who’s pushing 40. It’s also funny — and very on-brand — that the Gen Z character is horrified by the age factor but untroubled by the gender fluidity. The movie keeps becoming more of a head-trip as David (in Eva’s body) starts addressing his former self as Malia, and vice versa. 

Harari keeps the audience on its toes just keeping up with who’s who, maintaining a deadly serious tone as shit gets weirder and an element of paranoia creeps in that almost has a vintage Polanski vibe. If you are a stickler for story sense, it might drive you nuts that we never find out where the inner Eva ended up. And should we wonder about the significance of a Jew landing in a German’s body in the David/Eva switch? The female body occupied by David discovering she’s pregnant isn’t even the most extreme development, but it certainly adds to a gender identity conundrum that would set J.K. Rowling on a shrieking TERF warpath. 

The script veers in an investigative direction as the two protagonists start chasing clues after posting in an online forum to seek out others who have experienced a changement de corps. But those detours are less important than two superb scenes toward the end, both of which feed the sorrowful notion of looking at your own life as a stranger.

One comes as a result of Malia’s regret at missing her sister’s wedding. She watches the waterfront reception luncheon from a distance and plays out a scenario in her head in which she approaches her father (Romanian director Radu Jude, showing impressive acting chops), introducing herself in the body of David as his lost daughter. Bad idea.

The other, far more tender scene has David, still in Eva’s body, visiting his mother, Gabi (Valérie Dréville), saddened by the realization that she will never recognize him again. It’s those bizarre yet poignant moments that make Harari’s film so distinctive, along with the bold choice to film this quasi-sci-fi story just like any naturalistic French drama, with no stylized interludes and no woozy visual effects. The changes simply happen, and you either accept the movie’s terms, or you don’t.

Some may find The Unknown odd to a fault and too opaque to be satisfying. I can’t wait to see it again and keep sifting through its mysteries.