The guiltiest of guilty pleasures at the movies this week is the tough-as-nails "Lockdown," about bad things happening in the House called Big.

Though bracing and chilling, it's a trip to perdition the faint of heart and queasy of disposition ought to avoid. You need a hard head, a strong stomach and a willingness to watch the unwatchable. A 2,000-yard stare is a must. If you can't do the time, don't drop that dime.

The movie has two primary if crude virtues: First and best, it has an overwhelming sense of place. This extends to far more than the physical, those bleak corridors, the omnipresence of the cyclone fences, the echoes of footfalls and steel doors, the feel of suppurating institutional melancholy. It also includes the metaphysical aspects of the prison experience. When you saw the old pix -- even as brutal as Burt Lancaster's "Brute Force," probably the most violent of the American '40s pictures -- you knew somehow that you weren't quite getting the whole story. You can't crowd six hyper-aggressive, aberrant men in the space of a closet for 10 years without certain things happening.

Some years ago -- don't know why, don't know when -- the truth began to leak out about those things that happened. The prison was acknowledged for its secret vibration of haunting male fear: It was not only a zone of fisticuffs and gang turf war but, even more horrifying, it was a zone of rape. "Lockdown" gets that elemental reality in all its horror. It ain't pretty.

Second, more like its forebears, "Lockdown" boasts plot patterns, melodramatic story formula in full bloom and tendril, so reassuring when handled well, as they are well enough here. It follows three young men of varying degrees of involvement in criminal activity through a stretch in one of America's toughest prison systems, that of New Mexico. That's where some years ago the most violent prison riot in history took place, a far worse meltdown than at Attica.

The three are boyz in the 'hood, but each has a different orientation. Avery (Richard T. Jones) is a gifted swimmer, proud father of a son and is in love with his son's mother. Though a junior college dropout, he's up for an athletic scholarship that will get him up and out.

Dre (De'aundre Bonds) is a transitional figure. He has a job, even if an apparently dead-end one, but he's always looking for a little action. And finally, there's Cashmere (Gabriel Casseus), who's fully into the life. He's a dealer of dynamic demonism, his violent impulses occluded only occasionally by sentimentality toward his friends, particularly Avery. It's Cashmere who is framed by another dealer, but since Dre and Avery were in the car with him and they had discovered and handled a planted gun when the cops make the stop, all three end up convicted.

Though the film turns on a miscarriage of justice, that's not the subject proper of "Lockdown." It's not a screed against prison or the system or racism; it's about what is, not what can be done about it. It feels like a large hunk of truth, a grueling account of what it takes to get through the long days and the longer nights in a behavioral sinkhole where nobody wants to go, except the people who have a gift for the behavioral sinkhole.

Each young man's cellmate turns out to be his destiny. The lucky Avery finds a wise, compassionate con -- he has educated himself by reading Ralph Ellison's great "Invisible Man" -- who counsels him on the culture of the prison and how to survive it. Poor Dre is quickly sexually dominated by his cellmate and the whole tattooed crew; he's turned into a -- well, it is a term I would prefer not to use because I do so enjoy this very fine job. His whole sense of masculine selfhood is traumatized, with tragic consequences. Cash joins the posse of the boss black con, Clean Up (played brilliantly by Master P), which buys him initial survival but bends him further in the direction of crime.

The cast is superb, particularly Casseus as the tormented Cashmere. He has an complex part -- a young man pulled toward the criminal life, good at it, driven by a fury of anger and impulse, yet not oblivious to a larger moral responsibility -- and he makes that paradoxical personality believable. The young director John Luessenhop keeps the story jumping ahead, from atrocity to plot twist to atrocity. Occasionally, a last-minute reprieve or a sudden change of heart will arrive too conveniently and you can feel the strings being pulled clumsily. But what makes the movie memorable is its authenticity. It's not a trip to the multiplex; it's a sentence.

Lockdown (105 minutes, at area theaters) is rated R for extreme violence (including rape) and extreme profanity.

Dre (De'aundre Bonds) finds more action than he can handle in the searing "Lockdown."