February 26, 1999 | Late in Joel Schumacher's 8mm, the story of an accidental tourist in the lower circles of hell, there is a moment when private eye Tom Welles (Nicolas Cage) literally unmasks evil, only to confront something remarkably unremarkable. He can scarcely believe the ordinariness of the all-too-human face he sees. And the villain obviously enjoys his upending of the private eye's assumptions. "You were expecting a monster?" he tauntingly asks.

The savage irony of the scene underscores the provocative theme of 8mm, a frankly seamy movie that somehow manages to both exploit and transcend its scuzzy subject matter. Welles wades through the sewers of the porno netherworld at the behest of a fabulously wealthy widow, who wants to know if an 8mm "snuff movie" she found among her late husband's effects is a genuine record of a real murder. The plot turns on a familiar question: How far can you go into the darkness and still find your way out? But 8mm makes the puzzle unusually compelling by suggesting that a rational man must abandon any hope of fully comprehending the monstrously irrational. Or, as one character quips, "You dance with the devil, the devil don't change. He changes you."

Working from a well-crafted screenplay by Andrew Kevin Walker, who covered similar terrain in the even creepier Seven, director Schumacher takes time during the early scenes to establish Welles as a well-adjusted, white-bread family man whose only major vice is an inability to stop smoking. To be sure, his work as a "surveillance specialist" often calls for him to spend time lurking in shadows and photographing unfaithful spouses. But whenever the job is finished, he rushes back to his suburban home in Harrisburg, Pa., to savor domestic bliss with his wife Amy (Catherine Keener) and their infant daughter.

Welles has a reputation for diligence and discretion, two attributes that are highly valued by the widowed Mrs. Christian (Myra Carter) and her attorney (Anthony Heald). When summoned to the Christian mansion, our hero behaves with all the impeccably polite graciousness of an ambitious young man who senses the possibility of a big score. That is, he sucks up shamelessly. Told that he has been highly recommended by former clients, Welles smiles modestly and replies: "I've been privileged to provide services for people I admire." Eddie Haskell never sounded so smooth.

That smile evaporates very quickly, however, when Welles gets his first look at the grisly "snuff movie" in which a teen-age girl is eviscerated by a burly fellow in an S&M mask. (Schumacher wisely shows the audience just a few snippets of the horror show, leaving the rest to our imagination while we see Welles' appalled reaction.) Even so, the private eye remains convinced that the film is a fake, that snuff movies are nothing more than "an urban legend." Mrs. Christian desperately hopes that Welles is right. And she's eager to hire him to prove the young "victim" is still alive somewhere.

Cage is the very model of cunning understatement during the first hour or so of 8mm, a movie that feels all the more suspenseful simply because the often flamboyant actor is so subdued for so long.  As Welles traces clues that lead him to search for a long-missing runaway in the flesh pits and youth shelters of Los Angeles, Cage takes an internalized approach to his role, subtly undercutting the character's confidence with intimations of fear, disgust and loneliness. For a while, the flashier histrionics are entrusted to Joaquin Phoenix as Max California, a punkish adult-bookstore clerk who guides Welles through the sex clubs and porno flea markets where almost anything can be had, or filmed, for a price. "There are things you'll see," Max warns the private eye, "that you can't ever unsee." Squeamish moviegoers, take note: Max's words are meant for you, too.

By the time he connects with "the Jim Jarmusch of S&M," a flamboyant porno moviemaker named Dino Velvet (Peter Stormare of Fargo), Welles realizes he is in way too deep -- but has come too far to stop. 8mm might have been even more intriguing had Schumacher and Walker taken things a few bold steps further, to suggest that Welles, for all his disgust, might be slightly attracted to the perverse decadence in which he immerses himself. (Alfred Hitchcock likely would have emphasized the professional voyeurism that links the private eye and the pornographer.) The filmmakers stop far short of making that leap, but they do something almost equally daring: They refuse to make it easy for Welles to play the role of self-righteous avenger. Even when he has the chance to punish those responsible for a young victim's murder, he is impeded by the very morality that sets him apart from the people he despises.

Not surprisingly, Wade doesn't remain immobilized for very long. (If he did, audiences would start throwing things at the screen.) But Cage is such a powerful actor that you believe in the anguish of his moral qualms, just as you believe in the emotional pyrotechnics that he ignites after a slow and steady build-up. Better still, you also buy the furious frustration Welles feels when confronted with the immutable logic of evil: "Why did he do it?" "Because he could."

No one in his right mind will ever mistake 8mm for a great movie. Even so, it earns the right to be taken more seriously than you might expect. The supporting players are exceptionally well-cast -- James Gandolfini is aptly slimy as a porno producer, and Amy Morton is positively heartwrenching as the runaway's mother -- and the lurid milieus are convincingly detailed. But what really makes it work is the sense of urgency Cage brings to his character's sincere attempt to comprehend the incomprehensible.