The French have a deliciously helpful phrase for just about everything, and one of the best is nostalgie de la boue.

Nostalgia for the mud, roughly meaning an artist's or a reader's fondness for slime, muck, sewage, degradation, treachery and perversion. It's a specialty of the comfy bourgeoisie, who yearn for the real and the raw as experienced through the lens of literature or cinema. As far as actually, ick, touching the mud . . . no thank you. But of this set of folks who demand to live life fast, hard and safe (I proudly count myself), who among us, even the non-French, could not love the new policier "Narc," which represents nostalgie de la boue carried to extremes. It is a veritable boue-bath, a boue-wrasslin' match, a ghostie that leaps out and goes boue in the night.

Clearly, then, its virtues will be the virtues of mud: that is, filth, real and metaphorical, rawness, savagery, the law of the jungle as enacted in the gutter, all in the chilled and grungy city of wintertime Detroit. The weather is cold, the language is profane, the action is hot.

The movie revolves around a single issue: the death of an undercover cop. To solve the apparently unsolvable case six months later, the suits of the Detroit police draw on a certain bad boy, an edge-dwelling undercover stud named Nick Tellis, whose last bust went sour when he, uh, shot a pregnant woman (la boue, c'est Nick!). Even his marriage is mired in the boue of broken promises, uncommunication, bleak hopes. Nick is played by the moody looker Jason Patric, whom I would like a lot better if he'd put a k on the end of his name and if he weren't so damned serious about being taken seriously all the time. But fortunately, he's not the real story here.

Nick is really just our entryway into the private hell of Henry Oak, played by Ray Liotta at a pitch of psycho fervor it takes a true demon to achieve. Henry is your typical angry white guy chafing against job disappointment, lack of respect and too much alcohol -- only he has a badge and a gun and an attitude as brutal as a truncheon. He is hellbent on solving the murder of his former partner, but like a sports franchise owner, he wants to do it his way. That involves a lot of yelling, a lot of intimidation, a lot of saliva-dense explosions of spectacular profanity, and even an occasional back of the hand or butt of the gun applied somewhere soft and tender.

You think you've seen this one before? I thought so, too -- it had to be the one about the delicate liberal who helps the hate-filled bigot see the light. The best thing about "Narc" is that the only light is the gleam of stagnant water in the sewer. It turns out that Nick isn't particularly upset at Henry's frequent indelicacies; he's seen too much to take it very seriously, and he understands that the world in which they operate is pretty much populated by scum. So he sees Henry's attitude as a kind of extra level of Kevlar.

They interrogate, they investigate, they interview. Little things don't add up, and possibly Henry is trying a little too hard to lead the investigation over here when it should really be going over there. And he keeps turning up in the oddest places, like the home of the dead cop's wife, where he's suspiciously familiar. Hmmmm.

But the movie isn't selling plot. What it's selling is boue. That's all it sells, that's its only product -- a sense of urban life as a firefight inside a battle locked in a campaign, waged by men who have two choices: alpha males or omega corpses. You can get a sense of the milieu that the writer-director Joe Carnahan creates by looking at the names of some of his characters listed in the cast: Strung Out Man, Meth Dealer, Strung Out Woman, Porn Shop Dude and my favorite, Ruiz's Smoldering Squeeze.

It's a shame such attention to detail wasn't directed at the story. Or maybe the problem is the opposite: Too much attention to detail is directed at the story, and too many times various theories of the death unspool in flashbacks that are rooted in nobody's mind except the writer-director's. It finally more or less implodes on itself, winding up in an unpleasant sequence in which the two white cops speak impolitely to two handcuffed African American men in tones that could be charitably described as "louder than hell." There's also cursing, spitting, screaming, swearing, cursing, crying, beating and finally, cursing, spitting, cussing, profanity and bad language, as well as a lot of swear words.

One doesn't leave "Narc"; one is finally released from it. You feel beaten down by the film, till no spark of life remains. As I walked out, I felt like someone had just taken the cuffs off. It's a stunner that sadly grows tiresome at the end.

Narc (98 minutes, at area theaters) is rated R for extreme profanity, misanthropy and violence.

Looking for a cop killer, the Detroit police employ two blunt instruments played by Ray Liotta and Jason Patric.