THIS MOVIE is 51 years old, but you can still imagine Jane Greer's lipstick, fresh and poisonous, on your collar. She's the dangerous woman who went off with Kirk Douglas's $40,000, and so Kirk hires Robert Mitchum to find her. He fetches up at a cafe next to a small movie-house in Acapulco - "then I saw her, coming out of the sun", and he realises that this isn't just about the $40,000. He falls for her, and he forgets about how nasty Kirk can be.

She warns him about that, and she has a self-pitying look that says, you're not going to trust me are you?, as if trust were a form of abuse. All he can say - or sigh - is, "Baby, I don't care." For this is Mitchum at his loveliest and most resigned, the angel of his own approaching end.

Coming out of RKO in 1947 and made for very little, Out of the Past is often cited as an axiomatic film noir. In Mexico, Greer and Mitchum only meet after dark - "We seemed to live by night," his voice-over says, alluding to the titles of so many other noirs.

The black-and-white photography is by Nicholas Musuraca (a name fit for a villain), and it is the epitome of shadowlands, in which sometimes we see no more than the damp shine of eyes, lips or blood. There's also a sultry, fatal love theme by Roy Webb that takes delight in raising hopes it can stub out. Not to mention the cigarettes! Quite apart from the central trio, there are unerring supporting performances from Dickie Moore, Steve Brodie, Paul Valentine, and a feline Rhonda Fleming.

At RKO in those days, everyone knew his craft and respected the rules of the genre without fuss. Years later, Mitchum liked to pretend he could hardly remember Out of the Past among so many other films. But this one is special, because of its script. The story came from a novel, Build My Gallows High (the film's original title in Britain), by Daniel Mainwaring. The script is credited to "Geoffrey Homes" (Mainwaring's pseudonym). But recent research in the script files at RKO shows that Mainwaring did a first draft, and was followed by novelist James M Cain, who did a revision. And then, the very stylised dialogue of the film came in yet another rewrite, by Frank Fenton.

The question is of some interest because the film is rightly famous not just for the sardonic wit and fatalism of the talk, but because so much of what is said is also an elaborate, comic reflection on talk, what people mean, and on how our various forms of communication are all unreliable. Indeed, the talk for talk's sake is nearly rococo, postmodern and camp. It's as if Noel Coward had rewritten Jim Thompson, and it supplies a mocking framework to the hard-boiled routines. I don't know a film made so early that is so intent on teasing the way it's being made.

That brings us to Mitchum, and what made him unique. When the novel was first published, Humphrey Bogart tried to get Warner Brothers to buy it as a vehicle for him. Years passed, and it ended up at RKO. Mitchum was younger, more deadpan, more serenely hopless than Bogart could ever be. A year earlier, in The Big Sleep, Bogart cracked terrific jokes; but in Out of the Past, Mitchum acts as if laughing at jokes is indecent, or a waste of energy. He didn't give a damn, and let that show - with the result that he still looks the most modern of actors, utterly unconvinced by the flim-flam.

There's another man to remember in Out of the Past. Did such a script, such players, and the great Musuraca need direction? Of course, they did. And the director was Jacques Tourneur, a man who made fine adventure movies (The Flame and the Arrow), horror pictures (Cat People), and movies like this with the same ease. He was the son of Maurice Tourneur, one of the visual story-tellers of silent film. There's a modest grace to nearly every shot in Out of the Past - it's like whatever it was that Bobby Moore had in his prime, the trick of just knowing where to be for the best view.

'Out of the Past': NFT, SE1 (0171 928 3232).