Long before Kate Hudson lost him in ten days or Jennifer Garner was a girlfriend past, Matthew McConaughey was looking at the start of a "serious" movie career. He blazed with righteousness in A Time to Kill, orated with even more righteousness in Amistad (he had a thing for lawyers), and balanced that out with sneaky turns in The Newton Boys and EdTV. He was humming along for a couple of years there, fashioning himself into something like a new Paul Newman, but then... Well, then something happened. In 2001 he starred opposite Jennifer Lopez in The Wedding Planner and, other than forgettable turns in the dreary Frailty and Reign of Fire, he suddenly turned and barreled down a chipper but oddly gloomy road of shallow, glossy romantic comedies and fruitless attempts to become a mellower Harrison Ford. (See: Sahara. Actually, don't.) He muddled on like this for a decade, burying all that early promise under a pile of lazy choices. Eventually his improbably bright innate shine began to dim and he seemed to be, at just a little past 40, pretty much over. But now, suddenly! Matthew McConaughey is back, reversing the trend of the past ten years and becoming a real, honest-to-goodness Serious Actor all over again.

For those of you doubting the likelihood that McConaughey, drawling king of the cruddy '00s romantic comedy, can reinvent himself as a serious actor, as seems to be the plan, well, doubt no longer. This career makeover turns from fascinating prospect into thrilling reality with Killer Joe, a truly filthy film adaptation of Tracy Letts' 1993 play. In the film, McConaughey plays Joe Cooper, a dirty Dallas detective who moonlights as a contract killer. This is not merely some grim opportunist, though. There's a hard glint of something far more sinister in Joe's eyes, and pretty quickly in everything else about him too. This is Matthew McConaughey as a terrifying, straight-up psycho. And the results are as good as the idea seems, well, crazy.

Joe is hired by a low-life family — shaggy gambling debt-ridden son Chris (Emile Hirsch), his addled sister Dottie (Juno Temple), their hapless dad (Thomas Haden Church), and his dilapidated second wife Sharla (Gina Gershon) — to kill Chris and Dottie's mother. The plan is to collect on her $50,000 life insurance plan, the payout of which is to be divided three — or is it four? — ways. Chris desperately needs the money, as a friendly-yet-menacing bookie is looming over him, looking to collect or else. So Chris brings in this mysterious and business-like Killer Joe, who calmly lays out the rules of the arrangement and sets his price. It's steep, a whopping $25,000, but these folks are desperate, so they agree. The only hitch is that they don't exactly have the money to pay Joe up-front. No problem, says Joe. He'll just take little Dottie there as a retainer. That's the first sign that something's a little off about this darkly dressed, leonine mystery man. It, of course, is not the last.

The bulk of Killer Joe is built like a standard things-go-terribly-awry small-town crime thriller, but because it was written by a young, sensational-minded Tracy Letts (who here adapted his own script) and is directed by The Exorcist's William Friedkin, the NC-17 rated action reaches the Grand Guignol by the end. The film has a jerky pace to it, lurching and twisting from simple, well-considered stretches of dialogue in the beginning to the horrifically violent, agonizingly unrelenting final set piece. I suppose you could forgive the irregular rhythms of Killer Joe as merely the reality of turning a play into a film, but there have been plenty of smoother stage to screen adaptations in the past. Hell, Friedkin has done it better before, with 1970's seminal (heh) Boys in the Band and a TV movie version of 12 Angry Men in 1997. Instead I think the problem is that the filmmakers are simply eager to get to the part where Matthew McConaughey gets really bad. Sure all this other plot is funny and gritty and all, but let's get to the really good stuff. And, well, it's hard to blame them.

McConaughey does a beautiful, terrifying slow burn; watching his familiar laid-back graciousness curdle into stoniness and then explode into animal fury is wholly unnerving, like watching the kindly family dog go rabid. That's the meta attraction of this film — we're not simply watching Joe transfrom from polite but roguish good ol' boy to roaring demon, we're watching the actor himself trash that old easy-goin' caricature. McConaughey bravely sets fire to himself and ignites terrifically. It's going to be thrilling to see who or what rises out of the ashes. (We'll get to find out in The Paperboy and Mud, among other upcoming projects.) The rest of the cast gamely tries to keep up with this immolation and rebirth, but most fall short. Emile Hirsch, normally an appealingly clever performer, spends too much time whining and barking here. That petulant rude boy stare he's relied on so well throughout his career works for this film's more comical moments, but when the going gets really serious it doesn't quite match the stakes. Church and Gershon play their trailer trashers with a stock character rigidness, though Gershon, who is a bit miscast here, at least gets to leak all over the place in the film's gnarly climax. Temple, a wily little up-and-coming British actress, brings a welcome dash of wisdom to an otherwise fairly standard whispery weird girl role. (What is it with male writers, playwrights especially, and this particular young woman character? And what should we call her? The Infantilized Sexpot Mental Patient? Doesn't have quite the same ring as Manic Pixie Dream Girl.)

As a larger film, Killer Joe is a mostly forgettable sick joke. The film showcases some pretty ugly treatment of women and a too-cavalier attitude toward shocking violence, neither of which are justified by the end, but ultimately it doesn't stick with you in any resonant way. Once the "Ta da!" Aristocrats-level grostequerie of the finale is over, you shuffle out of the theater with a "Welp..." and a guffaw or two, and that's about it. But McConaughey does linger, sticks in the mind like hot black tar. This new being he's creating is mesmerizing. I doubt he'll go this hard every time out in his career 2.0, but he probably at least had to scorch as much earth as he could on the first try, in order to break out of that hard candy shell he'd encased himself in over the years. Welcome to the world, new McConaughey! It's maybe a grim place, but at least it's not Fool's Gold.