MyAnna Buring in KILL LIST (IFC Films)

British director Ben Wheatley’s heady genre mashup Kill List is how midnight movies are supposed to be: smart, weird, and extremely disturbing. A scene late in the film has a man cornered in a dark sewer, forced to shoot point-blank waves of shrieking naked cultists with flabby bellies and sagging breasts. It’s the kind of stuff that can permanently ruin the sexuality of any poor kid who sneaks into the film mistakenly hoping for a Jason Statham beat-’em-up.

Wheatley, who co-wrote the film with his wife, Amy Jump, stirs a witches’ brew of genre influences. You have elements of a Don Siegel hit man movie (with the contrasting quirks of two humanized killers) and the pained, methodical bleakness and staccato, jump-cut rhythm of cinema vérité ; and, well, the original version of The Wicker Man. Roughly, the story goes like this: after a botched mission in the Ukraine, Jay (Neil Maskell), an ex-soldier turned hired killer, is stewing at home in Britain with his Swedish-born wife, Shel (MyAnna Buring), and his young son. His best mate and fellow hit man, Sam (Harry Simpson), and Sam’s mysterious girlfriend (Emma Fryer) stop by one night for a rather strained dinner party, which ends with the two men grappling each other—they’re the kind of Fight Club guys who bond through drunken brawls. The visit isn’t only a friendly one, though: Sam brings news that they have a job. Soon, they meet up with the rather generically sinister head of the shadowy organization they work for, who has tasked the two men with three contract killings. Their mission begins matter-of-factly enough. The first mark is a priest, but something is not quite right, and by the time the tale ends, they’ll be fleeing those naked cultists through the sewers.

And what’s not quite right? That’s the movie’s real question. Suffice it to say, the answer probably lies more with Jay than with his job. The cracks appear early on. Near the beginning, he finds the remains of a rabbit left on his lawn by his cat, and he promptly fries it up and eats it. Later, he has an eczema breakout a doctor strongly hints is imaginary. And why, on one of his missions, does he see his friend’s girlfriend waving at him in the hotel parking lot at night? The break in reality is emphasized by Jim Williams’ eerie, wailing score, tellingly more fitting for a movie about demonic possession than contract killers.

I usually find the did-it-all-happen-in-his-head-or-didn’t-it? gimmick tiresome, but not here. Partly, that’s because the cast, who apparently improvised some of their lines, are excellent, with Maskell and Buring making a believably oddball family, and the film sustains a powerful atmosphere of dread and discomfort, with just the right leavening of raw black comedy. It remains gripping even in scenes that tread dangerously close to the ridiculous. I can more or less see what Wheatley was getting at in his interview with The Guardian last year, in which he said, with his film, he was hoping to tap into some of the unease in Britain right now over foreign wars and economic woes. It’s not that he made a message movie, or if he did, the message is in the mood: dank, repulsive, and vague.