For the thoroughly unpleasant "8mm," Nicolas Cage does a 180 from his performance in his last intolerable thriller, "Snake Eyes."

The previous film boasted an eye-popping, over-the-top attempt to distract us from its nonsensical cluelessness; in this one, Cage plays it so grave and depressive that our attention repeatedly drifts away from him. We end up wallowing in "8mm's" deviant, clammy atmosphere.

It's not anything you want to be exposed to for extended lengths of time.

Cage plays Tom Welles, a working-class guy whose impressive self-control and discretion has lifted him up to the status of Pennsylvania high society's favorite private eye. Married to a well-bred writer (Catherine Keener) and the father of a baby daughter, Welles lives in a picturesque little house beside a pleasant, woodsy creek.

That he doesn't seem to mind spending much of his time away on business and gets a kind of perverse pleasure out of lying to his wife about quitting smoking would perhaps indicate some dark resentment roiling beneath Welles' buttoned-down veneer.

But nah, the script does take Welles on a nightmare journey in which his assumptions about himself are confronted and tested, but what's revealed is a pretty simple, standard bent for self-righteous vigilantism. Writer Andrew Kevin Walker doesn't bring out the complexities of motivation he got at in his superior script for "Seven," let alone the kind of character contradictions initially hinted at here.

Anyway, Welles is hired by a super-wealthy widow to quietly investigate a reel of film depicting a teenage girl apparently being murdered — the proverbial "snuff film" — that was found in her late husband's private safe. She wants reassurance that the sick production was staged, that the unknown girl is still alive. Money, of course, is no obstacle, so the case becomes Welles' quest.

An extended stretch of detective grunt work leads Welles to a tentative identification of the victim, then to the film's best scenes: meetings with the long-missing girl's sad, lonely mother, magnificently played by Amy Morton as a woman whose hopelessness gives her a strange kind of sustenance. The trail then meanders to Hollywood's porno underworld, where Welles descends deeper and deeper into the purgatory of extra-legal fetish stuff: hard-core domination, kiddie porn, fake snuff.

His guide through these circles of desire is Max Hollywood (Joaquin Phoenix), an aspiring musician and adult-bookstore clerk who proves a resourceful, goofy font of hidden knowledge. Welles eventually locates a sleazy, X-video producer (James Gandolfini, overdoing the ooze) and a New York director of bizarre "specialty" films (Peter Stormare, overdoing everything). From there, things get bloody, obsessive, demented . . . but not necessarily any better than the low-key passages that dragged on before.

The director is Joel Schumacher, best-known for his "Batman" sequels and John Grisham potboilers. He is obviously reaching for something deeper and more stirring with "8mm," but the execution is too often superficial and confused. A film with this kind of degraded subject matter has to be sharply insightful and resonate deeply, like a "Boogie Nights" did, to justify itself. Otherwise, it just comes off as exploitative.

You can see Schumacher trying to get at something serious throughout "8mm," but he's overwhelmed by the film's tawdry elements. When you roll around in this stuff, it's hard to not look dirty.