Rewind

When I came to... is a classic refrain of hard-boiled detective fiction, with gumshoes forever being knocked cold by saps, brass knuckles and other blunt instruments. Their efforts to reconstruct the events before and after blacking out offer a kind of miniature of the entire genre, which hinges on the search for truth in dark corners.

Christopher Nolan's ingeniously twisty Memento could be a feature-length variation on this theme. Nolan's movie turns on two inventions, one a character trait, the other a structural tic, and part of the film's great fun is how each inextricably informs the other.

When an unknown assailant rapes and murders the wife of Leonard Shelby (Guy Pearce, sharply focused), the claims investigator sustains a head injury with strange consequences. He no longer has short-term memory — he remembers who he is, how to drive, everything before the accident, but can't create new memories that last more than a few minutes. He's still dedicated to finding his wife's killer, relying on a network of reminders. Polaroid snapshots tell him what he drives and where he lives, while more permanent instructions are tattooed across his body (a la the illustrated Robert De Niro in Cape Fear).

Memento's first shot shows a close-up of a Polaroid growing gradually more faint, and we realize the film is running backward. A gun leaps into Leonard's hand, a bullet flies back into the barrel, a crumpled body rises from the floor. The scenes soon run in the proper direction, but the prologue sets the tone that the film's action will unfold in reverse-chronological order, like Harold Pinter's Betrayal.

Each scene lasts more or less the limit of Leonard's memory, with the ending of one sequence having been the beginning of the previous one. Thus, step-by-step, we retrace Leonard's actions that led him to the introductory killshot. The audience, like Leonard, is kept constantly off-balance as he finds himself in unknown situations and must figure out what to do from context. We grow eager to find out such things as how Leonard got the two parallel scratches on his face — the foreshadowing is all.

The Dana Carvey vehicle Clean Slate had a similar premise, and Nolan takes advantage of Memento's comic possibilities. At one point, Leonard finds himself running through a trailer park, and his voice-over wonders, "OK, so what am I doing?" He sees another man and pursues him, thinking "I'm chasing this guy." When the dude fires at Leonard, he realizes, "No, he's chasing me."

No one can be trusted in film noir, least of all friends or lovers, and since everyone's a de facto stranger to Leonard, the film ratchets up the paranoia to exhilarating levels. We quickly suspect two of Leonard's closest associates, cagey Natalie (Carrie-Anne Moss) and chatty Teddy (Joe Pantoliano, looking like Cliff Clavin from "Cheers"), especially since the back of the Teddy snapshot has the note, "Don't Believe His Lies." Nolan gradually shows that Leonard can be dangerously manipulated not just by other people, but by himself.

As we follow Leonard's investigation on its backward trajectory, Nolan intercuts black-and-white scenes of Pearce in a seedy motel room, recounting a story from before his wife's murder about someone else's comparable case of memory loss. And we occasionally see brief flashbacks of his late wife (Jorja Fox), complicating the mix.

Though it's not the easiest of films to follow, Nolan crafts his narrative with such care that the audience soon falls into its rhythm. At the end Nolan seems to bend his own well-established rules, and the finale may make your head spin — counterclockwise, of course. But it's in the service of a deeper meaning, allowing Memento to conclude on an unnerving note about obsession, vengeance and grief that gives it thematic staying power beyond its gimmick.

Memento promises to be a cult hit, and not just for the cleverness of its conceit and the hip credentials of its cast (Pearce was in L.A. Confidential, Moss and Pantoliano in The Matrix). It's precisely the kind of tricky thriller that demands a second viewing after you know its secrets: The Usual Suspects and The Sixth Sense showed how popular such films can be. (Maybe the DVD will give viewers the option of watching it back to front.)

And like the most gleeful of thrillers, Memento leaves the audience with a creepy feeling that's difficult to shake. People will want to go back to appreciate Nolan's mnemonic devices — which may be demonic ones.??