In Chris Nolan's ingenious thriller, Lenny, played rather well by a ravaged, animalistic Guy Pearce, retains what little he can through a succession of Polaroids and gnomic notes, scribbled either on the back of his precious pictures or scratched into his own flesh. You have to have a system, he says, when every day you wake up in a strange room.

Nolan's set-up (from a short story by brother Jonathan) is intriguing enough then, but his coup de grace is to ally Memento's elaborate psychological conceit with a positively Roegian structure: the film is narrated backwards, from watching Lenny's final photo fade away before our eyes, to the bullet used to messily dispatch the murderer leaping back into his gun. Never fear though, it's only here that Nolan physically runs time in reverse. Once established, the film leaps back in bite-sized chunks, then plays itself forward until the narrative overlaps, intercutting with an apparently real-time monochrome mini-narrative of its own; it effectively locates the cinematic equivalent of Lenny's brittle mental state. It is, therefore, as much a film for the sturdy of mind as the strong of stomach.

Complicated in a uniquely satisfying way, Memento reminds us of The Usual Suspects in its attempt to redefine noir for the present day rather than parrot the past. Except that Nolan maybe has the edge because in the end this is far more than just a shaggy dog story; Memento has the emotional underpinning Singer's picture lacked. You feel for Lenny as you come to appreciate the desperation in his plight. He survives through a string of systems, but even they are of little defense against the manipulation of those around him. Those he meets along the way - Teddy (John Pantoliano), who we just saw executed; Natalie (Carrie-Anne Moss) - have agendas that often run contrary to his quest. What is the point of finding the murderer anyway, she asks, when in a few minutes he'll have forgotten again?

This is not the first time the technique's been used of course (Jane Campion's charming, if little seen debut Two Friends is told in reverse), but few films are so successful in pulling such a narrative off conventionally, let alone making things deliberately difficult for themselves. What it provides Memento with, though, is a fearful symmetry. With its physical trajectory so obviously reversed, Nolan's screenplay brilliantly succeeds in pushing its emotional one in a far more conventional direction. When you get to the end - or is it the beginning? - you appreciate that the problem we've spent two hours unraveling isn't the one we initially thought; that that solution, in a sense, already existed. Instead of getting less complex, Nolan's screenplay reweaves the threads even as it unpicks them, rendering Lenny’s situation even more emotionally perilous, and Nolan’s dazzling film a virtual Rorschach of cause and effect.