Have you ever had a nightmare in which you’re completely sane, just fine, in fact, but you’re confined to a mental institution, and you can’t convince anyone that you don’t belong there, don’t need to be there, and should be set free? I asked several friends and family members if they’d had that dream, and they said they hadn’t, but I sure have, and it’s a scary one. Well, that’s the premise of Stephen Soderburgh’s new film, Unsane. As you can imagine, it was a movie that I found more than usually compelling. Can’t wait for the filmmaker to make a movie about an actor who finds himself on-stage in a play, only he doesn’t know his lines or even what the play’s story is, plus he’s naked. I’ll pass.

Anyway, Claire Foy plays one Sawyer Valentini, a young single woman with what appears to be a responsible job in a big company. She’s really good at her job, though when her boss compliments her, it feels creepily #MeToo. Her social life seems to consist of one-night stands, but the only one we see her on ends so disastrously we’re not sure if it’s habitual or a one-off. She’s haunted by memories of a stalker ex-boyfriend, and we later learn that his stalking was so persistent and terrifying that she’s moved to a new city, gotten new phones and email, and cut off friends and family.

So she goes to a psychiatrist (Myra Lucretia Taylor), and thinks she’s really made a connection with her. But after her session–when the counselor seems peculiarly insistent that she sign various papers–a nurse takes her to an examining room, which she protests as unnecessary; she finished her session, and needs to get back to work. She’s told to strip, to put on a hospital gown, which she resists a bit, but what the heck; maybe this is procedure. And then she’s told that she’s self-committed to this facility, and will be reevaluated in a week. And there she is, stuck. A perfectly sane person, committed to a mental institution.

But how sane is she? (What do categories like ‘sane’ and ‘insane’ even mean?) Foy is a marvelous actress, and we’re never quite sure with her. She lashes out, hits fellow inmates and nursing staff, refuses her meds. I’d probably do all that. But she also recoils from one orderly (Joshua Leonard), insisting that his name is not George; it’s David and he’s her stalker. You do wonder. Sometimes she seems to have it together. And then, not so much. It’s the kind of thing Soderburgh is good at; paranoia, Kafkaesque bending of reality. It was shot entirely using a cell phone camera, which gave it just that tiny phenomenological edge.

An uncredited Matt Damon makes a brief appearance, as does Amy Irving, playing Sawyer’s Mom. But the movie really relies on Foy to carry things, and she’s spectacular. If you remember her from The Crown, it’ll take you about ten seconds to adjust to hearing her with an American accent, which is spot-on. And Leonard is just a little too aw shucks nice guy as David/George; you wonder about him too. Two excellent performances at the heart of the movie.

The movie doesn’t sustain that sense of unreality. I won’t give away the ending, but in the end, it became kind of disappointingly literal, explaining just a bit too much of its own plot cleverness. Much of the problem revolves around the character Nate (Jay Pharoah), a fellow inmate/patient who she befriends, who, it turns out, is an undercover reporter working on a story about for-profit mental institutions who commit sane people and keep them until their insurance stops paying. It’s not Pharoah; he’s terrific. But it feels almost like this movie about the shifting nature of reality suddenly turns into a journalistic expose of failures in our American mental health system. That subplot threw the movie off a bit for me; not the actors’ fault.

Still, it’s a disturbing and powerful suspense movie. If bad language bothers you, don’t bother; otherwise, it’s worth seeing.