Out of the muck and mire of human depravity that is “Killer Joe,” something magnificent comes: a killer performance by Matthew McConaughey.

The actor already has had a stellar year playing lowlifes. But his dirty Dallas detective Joe Cooper, who has a lucrative sideline as a hitman, is arguably the best of the worst.

Never has the actor’s molasses drawl been more lethal.

Never has noir been more diabolically naughty, either.

The film, directed by William Friedkin and adapted by Tracy Letts from his play, is ostensibly about the complications of a contract killing. Chris (Emile Hirsch), a hapless drug dealer, has no prospects, an overdue debt to his supplier and an angry mother. Getting rid of mom and collecting the life insurance payoff seems the easy answer. But it will require help from the family: his grease-monkey dad Ansel (Thomas Haden Church), stepmom Sharla (Gina Gershon), and his slightly dazed and confused beauty of a sister, Dottie (Juno Temple), who is the sole beneficiary of the policy.

The desperation that drives the film and sends Chris to plead his case is there from the first frame. “Killer Joe” opens on a rainy night in a muddy trailer park that has never seen better days. A junkyard dog is straining at his chain as Chris frantically bangs on the door. When Sharla finally answers, she stands framed in dull light wearing nothing but a shirt and a snarl.

“Killer Joe” is a brash bid for a comeback from a director who has had many fallow years since his 1970s heyday. The tension-building that helped earn Friedkin an Oscar for 1971’s “The French Connection” and the satanic chill of “The Exorcist” in ’73 make their way into “Killer Joe,” but none of the restraint is here. That makes this toxic slice of Texas crime lore exceedingly hard to stomach.

Before you can pity the mother, there is a story about Dottie’s childhood that will explain a lot.

Though death hangs over the proceedings, it is not the end game. The film is more of a leering look at the way in which serious intimidation can lead people to submit to humiliating things and how far a filmmaker will push it. Dottie, played by Temple, is an actress who has mostly flickered through other films such as “Atonement.” Here, she is excellent at creating a dreamy disconnection, holding the focus as a woman-child. She’s the collateral Joe wants, because there is no money for his upfront fees. His slow but deliberate seduction of the 20-year-old virgin is as mesmerizing as it is wrong.

Chris is as close as the film comes to a good guy. Plot twists keep the pressure building, and the internal struggle between morality and expedience resonates in Hirsch’s flailing. When death finally does come calling in “Killer Joe,” it is horrifically brutal but delivered, like much of the other carnal carnage, with a punch line.

By far the film’s deadliest weapon is McConaughey. The way the actor leans into threats, dropping his voice, wrapping eloquence in sinister tones, is skin-crawling. And if the eyes are the window to the soul, you really don’t want to peer for long into his. It is not an easy performance to watch, but it is unforgettable.

The cast around McConaughey is excellent at capturing the ethos of down-and-out blue-collar life. There are moments of brilliance, saturated with the blackest irony. There are other scenes that are so twisted that the film becomes almost unbearable.

Letts tends to favor damaged relationships with deadly consequences. But with “Killer Joe,” it’s as if he has stepped into the abyss. Friedkin is just trying to work his way out of it. But with McConaughey’s virtuoso turn as a completely virtueless man, Friedkin may just have pulled it off.