If someone tells you that you're insane, does that make it true-or are we clearly the judge of our own sanity?

Steven Soderbergh's latest film, Unsane, is an experimental dive into the psychological complexities that make or break our mind-and it's a successful journey due to Claire Foy's dynamic performance as Sawyer Valentini.

The product of a troubling childhood, Valentini recently moved away from her family due to a stalker, David Stein (Joshua Leonard), that she couldn't shake off. In a new city with a new job, Valentini starts seeing David all over the place, which causes a minor breakdown. She makes matters worse than she visits a psychiatric center and admits that she can be suicidal. Once that happens, the ward has her sign papers that she doesn't bother to read, and before long, Sawyer is unable to leave the place. She's a prisoner.

Screenwriters Jonathan Bernstein and James Greer take a healthy privilege in the first hour of this thriller by toying with your perception of Sawyer. Is she insane or simply not taken seriously enough? Is David really a worker at this place personally troubling her, or is her mind causing her to see things? When Sawyer punches an orderly that she thinks is David and turns out not to be, matters get worse. She continues to lash out due to an erratic and untrustworthy nature, keeping the audience off-balance.

Soderbergh shot the entire film using an IPhone, and the experimental device works well in a film made to keep us slightly off-kilter and unsure of what we are seeing. The imperfection in the shots and the dark grays and bright whites of the cinematography serve the plot just fine and add some mystery to it. Sawyer befriends Nate (Jay Pharoah) and grows a couple enemies, including Violet (Juno Temple, cracking open a can of crazy and licking it clean), giving our protagonist an equal blend of security and uneasy opposition.

Around the one hour mark, the mystery is taken away and the movie switches gears to a standard thriller, setting up a survival of the fittest flick that plays well due to Foy. You may know her from The Crown or smaller parts in other films, but Unsane really gives the actress a juicy chunk of meat to bite into. Since you aren't sure whether to defend her or commit her in your own mind, Foy can play with that suspicion and dread, mixing a few speeds into a breakneck performance that really keeps the film from being a routine thriller-horror entry.

The final third of the film doesn't invent much. You know a certain character isn't going to stop and the other isn't going to get away Scott-free. Soderbergh's originality in shooting the film doesn't mean he's reinventing the way to shock an audience. That's why he brought Foy along. She is a revelation.

When you register what is actually going on, Foy will keep you glued to the screen. You don't love her Sawyer, but you also can't take your eyes off of it her either.

The pacing is solid, with the 99 minutes roaring across like a race horse instead of stopping for overstated reflection. The score by Thomas Newman, one of the best in the business, is fairly standard stuff. The look is depressing and clouded as it you'd expect.

True confession: I missed the press screening for Unsane, but I didn't scream larceny after leaving the theater (and movie) with my 12 dollars. It was worth the price of admission and the time. An unremarkable film held up higher by a remarkable performance.