"Eight Millimeter is a descent into hell," says its star, Nicolas Cage, "except we're in our own back yard. If you pick up a rock, you're going to find creepy, wiggly things that you don't like."

The "rock" that Cage's private eye, Tom Welles, picks up is a short 8mm film showing the gruesome murder of a young woman. An industrial magnate's widow discovered it in a safe. She wants to find out if it's a snuff film, so Welles is hired to venture into the sleazy world of illegal porn.

The murdered woman had been declared missing. Welles follows her trail to Los Angeles, where she had hoped to become a film star. There he meets a wannabe musician working in a porn shop (Joaquin Phoenix), who guides him into the quagmire. The investigation thereafter becomes an odyssey into Welles' own psyche.

"Welles is like a symbol of the collective consciousness of the US," Cage says. "He has a fascination with the perverse, but at the same time it makes him angry. It's like Nietzsche said: 'Be careful, when killing monsters, that you don't become one yourself.'"