My dear readers, at the risk of presuming a great deal about the mental condition of the general public, I do believe that questioning one’s sanity is a natural part of being a self-aware species. Why, I myself find some reason to suspect that I’ve gone a little soft in the onion about twice a fortnight. Only a few days ago I thought I’d had a significant break with reality after I witnessed a bodiless child head descend from the ceiling on gossamer threads, whispering softly of keys and doors and unnamable things that slumbered beneath our floorboards. But then my dear Penny Dee assured me that she had seen it too and my fears were laid to rest.

Sadly, these matters are not always resolved so easily, as is the case with Sawyer Valentini, (Claire Foy) who is given much cause to question her own mental state after finding herself committed to Highland Creek Behavioral Center, an institution for the thoroughly distressed. Though Sawyer insists that she never meant to commit herself and that her faculties are beyond reproach, her behavior provides some cause for self-reflection. Continuously asserting her sanity somehow does not sway a staff of medical professionals and her case is not greatly improved by her decision to assault both a staff member and an inmate on her very first day.

Sawyer’s situation becomes particularly stressful after she receives the impression that David Strine (Joshua Leonard), a man whose voluminous attentions drove her from her former life in Boston, has gained employment at the very institution where she is temporarily trapped. She finds him doling out medications, violating the terms of a restraining order and offering her gentle words of encouragement. No one seems particularly receptive to the idea that one of the staff members is secretly a stalker and since she has done little to bolster her credibility up to this point, Sawyer is forced to confront two equally unappealing possibilities -- either she has lost her mind and is well-suited for institutional life or she is quite sane and trapped in close quarters with a dangerous madman.

Unsane whipped up a fair bit of press after it was revealed that the entire production was filmed on a “smart” telephone, a model that I understand is quite popular. Though I am suspicious of any phone that can be transported from one house to another while retaining the same number, I heartily applaud the decision to embrace methods and technologies that other filmmakers might think beneath them. My schedule usually forbids any overlap with the operating hours of most businesses but I had the great privilege of seeing Unsane in the theater and let me say, being filmed on a diminutive device has not had any kind of diminishing effect on its cinematic power. The tension is maintained at profoundly uncomfortable levels for impressive stretches. Though every film is absorbing in its own way, I feel it necessary to state that I forgot myself and my life outside the theater entirely and that all my happiness briefly hinged on Sawyer’s fate.

Director Steven Soderbergh has assumed the mantle of practically every genre and sub-genre save horror. His restless creative intelligence has produced fluffy crime capers, grim revenge yarns, baffling indulgences, realist epics and winning tales of men who dance naked for financial recompense. It is of little surprise that he is as capable here as anywhere else. He slides in some respectful nods to Misery (1990). He upgrades Joshua Leonard, whose most notable performance to date was as one of the ill-fated filmmakers in The Blair Witch Project (1999), from horror victim to horror villain. And he proves to be adept at both conjuring bracing jolts of terror and sustained dread. If this is what the man is capable of on his very first horror outing, I can only hope that we will be treated to a second.

Unsane runs 98 minutes and is rated R for disturbing behavior, violence, language and sex references.