Let no one fault “Black Snake Moan” for any lack of hellacious whap-a-dang. The movie’s pulp fictive advertising campaign boasts that “everything is hotter down South,” and to prove it, the director, Craig Brewer, unleashes a thermonuclear Christina Ricci.

As a Tennessee firecracker named Rae, Ms. Ricci, once cast for more ironic exercises comes on like one of Russ Meyer’s rapacious mud-honies. She whams, bangs, stumbles, and sashays through the drama’s opening round as a walking provocation, a Dixie pistol in Daisy Dukes whose nymphomania — attributed to childhood abuse and engaged as a form of demonic possession — is at once her only source of power and the urge that threatens to annihilate her. She’s already had one fit today because her boyfriend (Justin Timberlake) has run off to boot camp.

“Cough drops or condoms?” asks a listless convenience-store clerk as Rae wanders by, delivered with a smoldering disdain that is soon revealed as maternal. Moments later, Rae is striding the white line of a two-lane blacktop that stretches through the pines. A semitrailer bears down, horn blaring. She flips it off. Freeze frame. Roll title.

Somewhere across town, a graying blues singer and farmer named Lazarus (Samuel L. Jackson) is in a juke joint asserting his own form of dominance. He’s got his little brother at the business end of a smashed beer bottle, about to exact vengeance for turning him into a cuckold. Like Rae, he’s so emotionally bereft that he’s capable of anything. And soon, both of them will find out exactly what that is.

Mr. Brewer, whose affinity for the lazy rhythms and hotbed vernacular of the deep South gave the pimp-made-good saga “Hustle and Flow” its crowd-pleasing kick, is fabulous at setting up his stories, but his movies may always be less than the sum of their first 15 minutes. By now, thanks to promotional hype that overplays the most “controversial” aspect of the plot, most viewers will enter the theater knowing that a drugged-up Rae gets raped and beaten, and Lazarus rescues her. He seeks to redeem and reform her wickedness by chaining this wild thing to his radiator, dragging out his old guitar, and letting that black snake moan.

That’s a really big check to write, and it bounces: The loaded scenario amps up audience expectations and never follows through, mostly because Mr. Brewer has something kinder, gentler, and more Oprahesque in mind for his finale, whose theme might better be expressed by Otis Redding’s “Try a Little Tenderness” than any blues refrain.

Racial tension, while implied, is here almost always as a case of white-on-white and black-onblack violence, and while much has been made of the supposedly shocking vision of Ms. Ricci writhing like Salome amid a crowd of sweaty black dancers at the local juke joint, it’s not like white people are strangers in such places. The real-life model for Lazarus was the late guitarist R.L. Burnside, who often played at a juke joint on a farm in Chulahoma, Miss. The night I visited, in 1992, there was a National Public Radio crew in the house. And nothing hollers Caucasian more than NPR.

Where “Black Snake Moan” often redeems itself is in Mr. Brewer’s eye for details: The chubby kid hawking Oxycontin at the outdoor kegger where Rae gets obliterated; the pack of Roi-Tan cigars on a shelf in the juke joint, the unfussy back-road landscapes out of William Eggleston and John Christenberry photos, the casual yet profound balances between Saturday night excesses and Sunday morning contrition, and the music, which revives the late Othar Turner’s hill country fife-and-drum boogaloo at a decisive moment and gives Mr. Jackson cause to jam with Burnside’s former trio, with whom he ably recasts another variation on the Stagger Lee songbook.

Ms. Ricci’s itchy, seizure-prone performance derives a lot from the Jennifer Jason Leigh school of actorly psychosis, but it may be more entertaining for reasons that are less than artistically noble. As underclass potboilers go, there’s nothing here in the same league as Barbara Loden’s performance in her own 1971 “Wanda,” which was recently issued on DVD. The downbeat realism of “Black Snake Moan” makes Mr. Brewer’s softhearted melodrama look cartoonish.