Available on DVD “Compliance”

Confining extremes of human behavior to a single, drab room, Compliance, the squirmy sophomore feature from the writer and director Craig Zobel, is a slow-motion punch to the groin. As such, it’s fitting that one of our first sights is a large "NO" stenciled in the parking lot of a fast-food joint in suburban Ohio: as the film progresses, the word becomes a silent mantra for viewers who can’t quite believe what they’re seeing.

Distracted by the challenges of a busy Friday, the restaurant supervisor, Sandra (a marvelous Ann Dowd), is further harried by a telephone call from a man claiming to be a police officer investigating a theft by Sandra’s young counter assistant, Becky (Dreama Walker). Middle-aged, a little worn and competent within the limits of a job that doesn’t require much critical thinking, Sandra agrees to search Becky and her belongings. But when nothing is found the caller (perfectly played by Pat Healy) becomes more demanding.

Alternating flattery and intimidation, he persuades the women that a strip search will save Becky from jail and earn Sandra the approval of her regional manager.

But that’s only the beginning. Based on a 2004 incident at a McDonald’s in Mount Washington, Ky. (and roughly 70 similar hoaxes nationwide), this psychological horror movie slithers rapidly from uncomfortable to unspeakable. And inasmuch as this level of sordidness can be handled tastefully, Zobel succeeds in expunging all titillation from Becky’s ordeal.

As her humiliations — and our incredulity — escalate, the director periodically allows us some relief, backing his camera out of the storeroom where Becky is confined to check on her mystified colleagues. Snapshots of greasy fries and slimy grills pump up the unsavory atmosphere, while Heather McIntosh’s ominous, cello-driven score plucks our nerves and stirs our stomachs.

Raising troubling questions about the influence of class and education on our response to authority, Zobel cares less about charges of exploitation than about making us feel the monstrousness of the behavior on view. (A sequence involving Sandra’s bewildered boyfriend, brilliantly handled by Bill Camp, teeters right on the edge of plausibility.)

But it’s Sandra herself who carries most of the film’s ethical baggage, her subtle resentment of her attractive prisoner complicating her apparently mindless actions. A brief coda emphasizes the character’s pathos — and wonders if obeying orders is ever a valid moral defense — but makes empathy no easier. And maybe that’s as it should be.