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Perhaps it’s time for the “magical negro” to retire. Just in recent years, this mythical figure has come to the aid of a number of cinema’s troubled whites: a golfer (The Legend of Bagger Vance), a shallow executive (The Family Man), an uptight attorney (Bringing Down the House), and The One (The Matrix-es). It’s like those commercials for car loans: In mourning? In prison? No problem! A wise black man (or woman) will soon be at your service, guiding you through this difficult period in your life. His own needs, meanwhile, will be pushed aside.

This stereotype has had plenty of work over the decades, and now it’s been tasked with perhaps its most tiring—and definitely most unusual—case yet. Black Snake Moan’s Lazarus (Samuel L. Jackson) is a graying Southern farmer and former bluesman whose wife just ran off with his brother. He’s angry, especially after she coldly tells Lazarus that she doesn’t love him anymore. Later at a bar, his bro assures him that he will always love him; when the meeting ends with Lazarus smashing a beer bottle on a pool table next to his brother’s head, it’s clear the dude needs a project to keep his mind off things.

Elsewhere in sweltering Tennessee, a young woman named Rae (Christina Ricci) is begging her boyfriend, Ronnie (Justin Timberlake), to stay home instead of going off to boot camp. As Ronnie is driven away by his best friend, Gill (Michael Raymond-James), Rae drops to her knees and sobs; soon, though, her sobbing turns to moans and whimpers, and she’s clutching at her head and hallucinating. Apparently, it’s a nymphomania attack. (Bet paramedics aren’t trained to handle that one.) Rae later says that each episode starts in her head and works its way, er, down south. She can’t control it—the only cure is to jump the nearest guy nice enough to do her.

So Rae has an afternoon romp with one of her standbys and later goes to a party where she drinks straight from the bottle, swallows pills, and plays underwear-and-shoulder-pads football before passing out and getting raped. Gill gives her a ride home, along with a lecture—her first post-Ronnie partner is black, after all, and that makes her cheating even more unacceptable. He stops the truck and gets ready to have a taste himself, at which point she taunts him. Gill responds by delivering a few quick blows to her head and kicking her, unconscious and nearly naked, onto the road. Lazarus spots her, and as sure as his name means “assistance of God,” he’s gonna rid her of her wickedness.

You may already know, if you’ve seen Black Snake Moan’s somewhat misleading advertising, that Lazarus tries to achieve his goal by chaining Rae to a radiator. Writer-director Craig Brewer hasn’t exactly made a traditional grindhouse film, though—­you see, this one’s a grindhouse film with heart. The story is a visceral experience even if you choose not to buy it. Ricci’s performance is remarkably and brutally physical despite her skeletal build: She’s a one-woman sex scene as Rae frequently goes into heats that match the palpable swelter of the backwoods town, and she’s a rag doll as Lazarus drags Rae back into his house whenever she tries to run away. (Like a dog, Rae once flies off as if she’s unaware of the restraint that then violently yanks her into reality.) Ricci conveys more mental anguish with one feral wail or pitiable attempt at seduction here than she did in her entire portrayal of Elizabeth Wurtzel in Prozac Nation.

Jackson, too, turns in a strong-as-steel performance that borrows from his roles in Pulp Fiction and Snakes on a Plane, crossed with nearly every character Morgan Freeman has played. Lazarus bellows scripture and orders Rae around, but it’s all because he just wants to help the child and because he alone knows how best to do so. It may not exactly be what Dr. Phil would recommend—again, you have to believe hard in the movie’s conceit—but Jackson manages to convey the character’s inherent decency.

Brewer revisits the music-as-salvation theme that propelled his previous film, 2005’s Hustle & Flow. Black Snake Moan begins with black-and-white footage of Delta blues singer Son House, who opines that the only true blues happens between a man and a woman. The Black Keys’ throbbing “When the Lights Go Out” follows, and it’s a sign of things to come; for all its physicality, the movie is never as alive as when there’s a guitar in someone’s hands. (Less impressive is the moment Lazarus sings to Rae with his hand over her face.) The use of the blues, however, makes matters tricky. It’s inarguably appropriate for the setting and for Jackson’s character. But the film’s most joyous scene also contributes to the ­heal-the-white-girl stereotype. Lazarus takes Rae to his hangout one night when he’s scheduled to play. Sheepish at first, Rae starts dancing with the locals until she’s happily grinding among them, sweating and smiling for the first time in the movie. Pretty much immediately afterward, Rae is renewed and ready to change her life.

Brewer’s script doesn’t take itself entirely seriously, but what laughs exist are nervous ones, such as when Rae semiconsciously calls out, “Lazarus! Get off me!” while she’s writhing on the floor—and his wide-eyed response is to grab the good book and run the hell out the door. Despite Lazarus’ good intentions and the inevitable revelation of Rae’s troubled past (sympathy is also expected for Timberlake’s otherwise forgettable character, who suffers anxiety attacks), the story is presented too harshly and, often, too ludicrously to be very moving. One more softly compelling scene involves a preacher’s conversation with Rae in which he asks, “What’s your heaven?” The problem is that until this late point, you probably didn’t care.