Despite some storytelling flaws, Unsane is ultimately suspenseful, terrifying, and rather haunting.

A scene featuring Claire Foy in “Unsane.”

Unsane, directed by Steven Soderbergh. Screening at AMC Boston Loews 19 and Kendall Square Cinema, Cambridge, MA

By Peg Aloi

It is entirely appropriate that Steven Soderbergh’s latest film is shot entirely on an iPhone. Personal technology makes invasion of privacy rather easy, after all. Although parts of the story are somewhat implausible, pushing this film slightly over the line from thriller to horror, any woman who has had to change her number or address to avoid a stalker will identify with the protagonist. Claire Foy (The Crown) plays Sawyer Valentini, her name clearly some sort of mash-up alluding to her penchant for lying as well as the romantic fixation that forces her into hiding.

In the opening scene, we see Sawyer working a high-powered job in a large eastern city. She’s not exactly friendly with her coworkers. She has a meeting with her boss to review her performance; his praise of her work in her first few months inspires him to invite her along on a business trip that she’s well aware she’s not yet qualified for. She’s creeped out by his inappropriate attention, yet fails to mention it when she calls her mother (the always wonderful Amy Irving), making her new life in a new city sound prosperous and exciting. That night Sawyer meets up with the guy she found via Tinder at a bar. He’s cute and seems nice, and they hit it off. She offers him some intimate fun at her apartment if he promises never to call or contact her ever again, which he agrees to. But, before things get hot and heavy, Sawyer has an anxiety attack and throws him out.

We see Sawyer googling “support groups for victims of stalkers” (ah, Google, the contemporary stand-in for clunky expository dialogue), and soon Sawyer is talking with an understanding female counselor. Sawyer confides she is often afraid, and talks about her history of having to change her phone number multiple times. She moved hundreds of miles from Boston to escape a stalker, even though she had a restraining order against him. Led by the counselor’s questions, Sawyer admits she has contemplated harming herself. When she goes to the reception area to check out, she’s told she needs to be examined. She is perplexed, but complies. In the examination room she’s told to remove her clothing and jewelry and, although she argues that she’s already fulfilled her purpose in coming to the facility, she once again complies. What unfolds next is perhaps a commentary on the social norms that encourage women to “be nice” when they should run away screaming.

At this point the first somewhat unlikely plot point is engaged: Sawyer is told she must remain under observation in the psychiatric clinic for a week because she admitted to having thoughts of self harm. Outraged and confused, she refuses to accept this and is manhandled by staffers who say they’re trying to keep her safe. The first couple of days don’t go well; she’s hostile to others and uncooperative. A friendly patient named Nate (Jay Pharaoh), who is also a group discussion leader, takes her aside after her first “sharing” session. He tells her that she is the victim of an insurance scam that will keep her there as long as her company will pay for it. She is shocked and furious, but Nate tells her there is very little she can do and she should make the best of it for the next few days. Sawyer’s phone has been confiscated; she wasted her only allowed phone call contacting 9-11. She hoped the police would remove her, but they dismiss her request — they get these calls several times a day. She notices Nate talking on his phone late one night when he thinks everyone’s asleep. She convinces him to let her use it and that she won’t rat him out. But viewers have figured the twist out, if Sawyer has not: Nate is a journalist working undercover to expose the insurance scam.

Sawyer calls her mother and explains the situation, and is reassured that mom will hire a lawyer who will get her daughter out of the facility. Mom is allowed to visit her briefly, but Sawyer knows she won’t be able to leave right away. Mom is annoyed that Sawyer didn’t tell her about the stalking incident. After the visit, Sawyer sees a staff member who reminds her of her stalker; she thinks she may be losing it again. Then she realizes it really is her stalker. He’s changed his name from David Strine to George Shaw. She frantically screams at the staff that she knows who this man is and that he should be arrested because she has a restraining order against him. But they don’t listen and she is again, ironically, restrained because she has gotten into a scuffle.

David politely and condescendingly denies Sawyer’s accusations; the staff believe him to be a model employee. His job is handing out medication and at one point he gives Sawyer something extra that causes hallucinations and violent behavior. Nate catches on and promises to help Sawyer after he leaves the facility. But David is as clever as he is ruthless, and begins to sabotage the rescue efforts of Sawyer’s tiny support system.

Claire Foy in “Unsane.”

As David, Joshua Leonard (who burst on the scene as himself in 1999’s The Blair Witch Project) gives a low key but terrifying performance. David’s obsession with Sawyer began when she volunteered at a hospice facility where his father lived out his final days. He acquired her phone number and started texting her constantly, forcing her to turn to the order of protection. David’s presence raises fuzzy plot timing issues. How did David know Sawyer would be at the facility at this time? How did he get a job there so quickly after her arrival? Despite the implausibility of this, and several other story elements, the film airily transcends its narrative inconsistencies by sheer force of, well, focusing obsessively on its protagonist. Unsane portrays a powerful portrait of what being a victim of stalking feels like: the terror generated when another human being insists on being romantically involved with you and won’t take no for an answer. Leonard is thoroughly convincing as a seemingly mild-mannered man who hides a sociopathic and ultimately violent interior.

Other performances in the film are equally arresting, including the oddly cast Juno Temple (Wonder Wheel) as Violet, a young woman who immediately targets Sawyer with harassment and threats upon her arrival. As Sawyer, Claire Foy embodies the depths and contradictions of psychological trauma, and the hidden strengths it can uncover. David ratchets up his game, removing Sawyer from public view, compounding the isolation she feels when it becomes clear that no one can help her. But when Sawyer turns the tables on him it’s chilling to behold.

Unsane draws on a number of familiar horror tropes that, while slightly absurd at face value, are nimbly manipulated in a way that serves the subject matter (stalking) brilliantly. Screenwriters Jonathan Bernstein and James Greer (the team behind The Spy Next Door and Just My Luck) spice up the grisly doings with odd touches of humor. For this film, Soderbergh acted as his own cinematographer and editor (though he uses pseudonyms in the credits — why?). Visually the film makes some unusual choices in terms of point of view and perspective which are somewhat confusing, but ultimately successful. Despite some storytelling flaws, Unsane is ultimately suspenseful, terrifying, and rather haunting.

Peg Aloi is a former film critic for The Boston Phoenix. She taught film and TV studies for ten years at Emerson College, and currently teaches at SUNY New Paltz. Her reviews also appear regularly online for The Orlando Weekly, Cinemazine, and Diabolique. Her long-running media blog “The Witching Hour” can be found at themediawitch.com.