“Hurricane Billy” Friedkin is getting his mojo back, with playwright Tracy Letts in the bucket seat. After their gonzo 2006 triumph Bug, the sick soul brothers reunite not for the Pulitzer-anointed August: Osage County, but Letts’s raunchy, rowdy 1993 debut. Killer Joe evokes the hardboiled regional poetry of Jim Thompson and William Faulkner (who supplies the obligatory poetic epigraph), flirts with outright exploitation, provides game actors with roles to relish, and finds the heart of darkness in a bucket of Kentucky Fried Chicken.

Their adaptation leaves the source text almost untouched. A few choice locations open up the Dallas, Texas outskirts but the real meat and inevitable massacre still occur in the pressure-cooker confines of a family trailer home. Cinematographer Caleb Deschanel employs a grease-stained Edward Hopper palette refracted by tawdry and cartoonish fluorescents, and the atmosphere is all noir jazz bassline, thunderstorms, blazing trash-can fires, restless pitbulls, and Gina Gershon’s casual crotchbearing. Letts convinced Friedkin to preserve this charming introductory detail in an eight-page memo bearing the advice “Don’t be afraid of the pussy.”

Meet the Smiths: paterfamilias Ansel (a hysterical Thomas Haden Church) is an oaf in a union suit, too lost in a haze of pot and monster-truck rallies to pay heed to the nude preening of his wife Sharla (Gershon) or the troubles of his hapless son Chris (Emile Hirsch). His daughter, 20-year-old babydoll Dottie (Juno Temple), is prone to sleepwalking out of her bedroom safe haven of snowglobes and stuffed animals to coo (occasionally lucid) non sequiturs. Chris and Dottie’s mother has been dipping into Chris’s coke stash, the sale of which was to pay off a debt to a local kingpin.

So it is decided, with minimal philosophical or logistical debate, that the conspicuously off-screen matriarch must die. A $50,000 life insurance policy can cover the cost of hiring the eponymous cop (Matthew McConaughey), who moonlights as a courteous hit man. The remainder is hardly starting-over money, not that any of these folks has a concrete plan beyond living a bit better than before. There is no on-screen rumination or reflection in this amoral vacuum, just savage emotions and primal call-and-response. These people aren’t too stupid to live, just too stupid to succeed.

Dottie is the virginal sacrifice in lieu of an advance for Killer Joe’s services. When Joe looks at Dottie, Friedkin backlights her unbrushed hair into a halo of hope amidst the crossfire of betrayals and bad ideas. McConaughey, after a 15-year Rip Van Winkle act, has awoken in a veritable auteur playground this year (starring in releases by Steven Soderbergh, Richard Linklater, and Jeff Nichols). He has taken notes from Robert Mitchum’s Night of the Hunter playbook, avoiding a fullblown cowboy-hat-and-sunglasses camp cartoon. Joe is both sadistic monster and angel of vengeance, greedy predator and tender lover. He is, perhaps, the hero of this sordid tale. Friedkin and Letts possess a bold oldschool faith in familiar pulp tropes and down-and-dirty dialogue, re-creating the sort of electric clash between hyperrealism and hallucination, horror and farce, rarely seen since the best B-movie emissions of Poverty Row. Such deep-fried depravity used to be a guaranteed seat-filler for a certain kind of audience, but these days, slapped with an undeserved NC-17, it seems downright avant-garde. Killer Joe closes with the disco-blues sermon “Strokin’” as Clarence Carter leads listeners in an ecstatic release of raw, rural libidinal energy. It is the perfect punctuation to this exuberant white-trash Gothic. Friedkin and Letts are similarly unapologetic about their noboundaries ride on the raging blue-collar id, and unafraid to play it for both laughs and genuine feeling.