Editor’s note: The following review contains major plot points, including discussion of the final scene.

William Friedkin’s smartly paced, deliciously watchable film of Tracey Letts’ 1998 play mines a rich seam of gothic Americana in its portrayal of a greedy, incompetent family tearing itself to pieces.

Like the director’s The Exorcist (1973), Killer Joe examines the effect of a malignant outsider imposing itself upon an American family unit. However, while The Exorcist’s devil was a distinctly uninvited guest, Matthew McConaughey’s insidious Joe may be one of the first bogeymen in cinema to be actively welcomed into a position of destructive power.

The obliging family are the Smiths, who dwell in a cramped, fetid Dallas trailer park home, and conspire in a doomed plan to claim the insurance money of soon-to-be-departed matriarch Adele. Detective/hitman Joe (the only character in the film with anything approaching a code of ethics), in lieu of cold, hard cash, decides to take daughter Dottie (Juno Temple) as, essentially, a sexual prisoner until the funds appear; a suggestion actively encouraged by the family. With the facial hair and mind of a goat, Thomas Haden Church’s Ansel (the dad) makes for a transcendentally dim, affectless foil to Emile Hirsch’s wheedling catalyst/capitalist son Chris; an inept, desperate whiner.

Friedkin coaxes some superb performances to bring this unpleasant world – and Letts’ earthy, astringent dialogue – to life. A lithe, imposing McConaughey palpably delights in the opportunity to shake off a decade of undemanding nice-guy roles. Following in a long line of morally ambiguous Friedkin anti-hero cops (think The French Connection’s ‘Popeye’ Doyle, Cruising’s Steve Burns or To Live And Die In L.A.’s Richard Chance), his Joe is simmering and sexy, with a transformation to messianic beast in the film’s long final scene that’s electrifying.

Through Joe, Letts seems to be brutally satirizing a particular idea of middle America’s dependence on Christianity. In a cleverly ironic perversion of Americana tropes, Joe adopts the cadence and fervour of an evangelical Southern preacher when subjecting Sharla to a grotesque sexual assault with another emblem of American consumption: the chicken drumstick. Note too the psychotic manner in which Joe attempts to impose Christian family traditions upon the Smiths after his brutal assault (“Now, who’s gonna say grace?”)

McConaughey is matched by Temple, who nails the required mixture of vagueness, innocence and allure to make the pivotal character of Dottie believable; their chemistry aids a plot strand that’s fairytale of the darkest hue. The virginal Dottie, prone to sleepwalking, seems to exist in the liminal space between wake and sleep, muttering vague aphorisms, and blankly recalling childhood traumas. Like some lost character from an Angela Carter novel, her inquisitive young mind, then body, is colonized by this handsome, authoritative agent of institutional corruption. He’s her prince and her wolf. Her lover and her replacement father. And, as the film ends, the father of her unborn child too? Their extended dinner date scene, filmed in long, unhurried takes, is a deliciously awkward, erotic, and troublesome moment. If, like Dottie, we’re being taken in by Joe’s charisma, that’s exactly what Friedkin wants.

Though the director indulges in some cliched play-to-film tropes (why must it always be dark and stormy outside?), he handles the thriller aspects of the script smartly and without fuss. Similarly, his rendering of Letts’ milieu is confident and concomitant with the thematic darkness and moral murk that marks the best of his canon. Unlike Justin Kurzel’s claustrophobic, singularly depressing Snowtown (2011), however, Killer Joe adopts a bravely comic take on a crumbling underclass in which the the moral goalposts have not so much shifted as disappeared from view entirely. In ironically peppering the frame with heartland Christian iconography (crosses and flags), Friedkin conjures a land where understanding of religion has gone to seed; where the extreme breakdown of family life is accelerated by the the characters’ aggressive, borderline-absurd adoption of conspicuously capitalist, ruggedly individualist values in the face of poverty and cultural breakdown.

Whereas Bobcat Goldthwait’s God Bless America(2012) explicitly cast television as the root of evil in contemporary society, Friedkin places the TV as an insidious opiate; a constantly distracting presence, flickering throughout countless scenes. Ansel is barely able to concentrate on pimping out his daughter, so engrossed and amused is he by the monster trucks on the box. It’s significant that Joe pointedly destroys the family television before his final rampage; one suspects that this material loss will affect Ansel more than that of his own son. (There’s no internet connection round these parts, meaning that Dottie can‘t even follow her beloved Justin Bieber – his image adorns her walls – on Twitter.)

However, Killer Joe falters when the script strives for American tragedy, such as Chris’ Steinbeckian lament about “raisin’ rabbits”. Chris’ late-blooming morality, though necessary to keep the plot ticking over, is the film’s least convincing element, unaided by Hirsch’s performance, which is the thinnest on show.

The best joke in this frequently funny film comes when Sharla (a brilliant Gina Gershon) picks at a loose thread in the shoulder of Ansel’s ill-fitting suit as they nervously await news of Adele’s life insurance policy. With very little resistance, the entire arm falls away. The characters’ plans – like their moral fabric – do not withstand much scrutiny, and Letts and Friedkin delight in poking away. In a recent interview, the director cited the Coen brothers as his favourite contemporary American filmmakers, and as the dust settles on the final carnage in the Smith kitchen, the mind can’t help but wander to that incredulous question posed by Fargo’s earnest cop Marge Gunderson: “And for what? For a little bit of money.”

Though at times here it’s tempting to see Friedkin as Jerry Springer with a camera – gawking at human detritus – there is a serious undercurrent that breaks through the black comedy; a sadness at the abject moral decay on show in this glum, savage middle America.

Killer Joe is in cinemas now.