Gaspar Noé's Irréversible comes at you hard. Early scenes take you careening down dark twisty hallways, deep inside a sex club called the Rectum. As the camera passes men in mid-sex act, the soundtrack roars and grinds, dragging you down even further, into the mind of Marcus (Vincent Cassel), as he seeks out "Le Tenia" (The Tapeworm, played by Jo Prestia). Their eventual confrontation, barely comprehensible, ends with Marcus' rape and Le Tenia's brutal murder, his head bashed in with a fire extinguisher.

While this early sequence is so overwhelmingly visceral that the specifics are sometimes incomprehensible, the film's much-discussed centerpiece -- Le Tenia's rape and beating of a beautiful girl, Alex (Monica Bellucci) -- is plainly displayed. For nine minutes, the camera doesn't move, just sets up on the floor of an underground pedestrian tunnel and watches. The scene is harrowing, visceral, uncommonly difficult, and it has educed vehemently polarized responses, from disgust at its explicitness, to awed respect for its nihilist daring and existentialist grandeur. Irréversible has nerve, that's for sure.

It also has outrage, fear and a severe, if skewed, sense of morality, at once uncompromising and irrational. For all its menace, for all its apparently scandalous cruelty, Noé's film, much like Eyes Wide Shut, his self-declared inspiration, is primarily an indictment of narrative conventions and belief systems, the ease with which violence is made thrilling and viewers identify with those who perpetrate it.

Irréversible's first scene establishes the ground for this charge, as the butcher Philippe (Philippe Nahon) -- the abusive protagonist of Noé's first feature, 1998's I Stand Alone -- recalls his crimes for an impassive, chain-smoking listener: "I was in the joint," Philippe says. "I slept with my daughter." "Ah," comes the simultaneously bland and profound rejoinder, "The Western syndrome."

The movie proceeds to unravel this syndrome, the guilt, desire and retribution that drive so many myths and histories. The plot unfurls in reverse, so that this first scene will become a kind of annotation on what comes after. The scene that follows is the first to show Marcus and his fire-extinguisher-wielding friend Pierre (Albert Dupontel), specifically, the consequence of their punishment of Le Tenia, the man who raped and beat Alex into a coma: Marcus is carried out of the Rectum on a stretcher, Pierre is hauled away in handcuffs, grimly bumping along the street in a police van.

The events that lead up to this pathetic and devastating finale are rendered in images increasingly legible, increasingly distanced from Marcus and Pierre's internal frenzies. It turns out that they share a sense of culpability, and act to redeem themselves, as boys tend to do in movies. Following a fight at a party where Marcus is particularly inebriated and obnoxious, they allow Alex, currently Marcus' girlfriend and formerly Pierre's, to leave alone. Upset, she elects to walk through an underground tunnel rather than navigate the traffic on the street above. Here she runs into Le Tenia, angry for his own reasons. The film's final moments, pre-rape, grant access to Alex's experience, the secrets she withholds from Marcus, as well as her (frankly, rather conventional) embodiment of life and hope.

This backwards structure has inevitably drawn comparisons to Memento, but where Chris Nolan's film sucked you up inside Leonard's traumatized mind, Noé's jumps from one character to another: the self-involved beau, jealous ex, the self-possessed object of their affection. Their very familiarity makes their sensational fates disturbing. Alex's anger at the self-involved Marcus has a source that he can't know; Pierre's continuing devotion to Alex shapes his relationships with both his friends, in ways that none of them articulates. And each makes choices that are irreversible.

The emotional (and ethical) catch is that, though they are unable to see beyond their separate, present moments, you know the results of their choices. Thus, Irréversible's most radical aspect is not its depictions of physical havoc and ferocity, but its more gradual mindfuck, its vengeance on viewers.

Delivering the end of the revenge plot first, the film undermines any standard emotional payoff: Marcus and Pierre's assault on Le Tenia doesn't offer up the same satisfaction as Willis, Eastwood, Snipes or Bush tearing up his sworn enemy, because you've been granted no investment in the mission or the characters. What you see at first is just violence, abstract and sadistic, only meanness and savagery and blood pulp.

Similarly, the rape occurs before you have met Alex, before you've even seen her face, except as it appears, ravaged and unrecognizable, on a stretcher, on the way to an ambulance. And, truth be told, the eventual obviousness of the context for these horrors, simultaneously cynical and melodramatic, is probably worse than its initial obscurity. Finally, you know there is no sense to what happens, no moral frame, no cause, except that Western syndrome, the meaning imposed on events by those with the capacity and nerve to interpret and so, own, it. Control, however, remains impossible. And that's what the Western syndrome will never acknowledge.