Film studies: What lesson did Truman teach us? You should never trust a writer...

There's a tart rejoinder to that way of thinking in Scott Fitzgerald's unfinished novel, The Last Tycoon. Fitzgerald must have tried that grand, disdainful speech himself a few times. After all, at the end the author of The Great Gatsby and Tender is the Night was living in Los Angeles, trying to get screenplays right, and with a mistress destined to become a gossip columnist. But Fitzgerald hadn't lost his wits. He knew writing scripts was a tough trick, and one real novelists should ignore.

He also knew how easy it was for writers who had taken the money and shelved their great works, to sound superior. So, in The Last Tycoon, the studio head Monroe Stahr has an English novelist on staff - a fellow named Boxley - who reckons he's above such things. And so Stahr tries to teach him to master the trick or go home. It's bad for the soul to live in a daft heaven while writing it off as hell. To which a real Boxley might say, "Never mind, Mr Stahr, you've no idea how corrupt writers are."

Such thoughts came to mind watching the deliciously acidic new film, Capote - for which Philip Seymour Hoffman is going to win the best actor Oscar on account of his brilliant trick, that of shrinking his rather bloated, coarse and macho self into the mincing persona of Truman Capote. That's what actors do, of course, and Hoffman is one of our best. But don't let his bravura impersonation put you off from the main point of Capote, which is to say, never trust a writer, especially if you're inviting him to dinner to meet your stupid friends. Rely upon it: in the end, the writer will behave badly.

As the film presents it, there is Truman, living in New York one day in 1959. He is 35, petite, high-pitched, flagrantly gay, known as a great Southern writer in the few quarters that cared, and as tough as - well, there's the point. In The New York Times, he reads about the slaying of a farmer and his family - the Clutters - in Holcomb, Kansas. He determines to go there, to examine this small local crime, to write about it, to make a new kind of book - a non-fiction novel, they will say. It is quite clear that he has his mind made up, without a jot of pity for the Clutters. The New Yorker will finance the trip and as a travelling companion and "girl Friday" he will take a childhood friend, Harper Lee, who has just finished but not yet published, her own book, To Kill a Mockingbird.

Lee is played by Catherine Keener in what could be the best supporting actress role. They board the train west, and a young porter (black) puts his head in their compartment to say what an honour it is to have Mr Capote on the train, and how the porter reads all his books. Truman glows like cream. Harper reflects, and then she gets it. "You paid him to say that!" she realises - it is the keynote moment to a film in which In Cold Blood proves to be not just a clever title, but a proper verdict on Capote himself. And that's the refreshing point: the writer is a shit.

I say "refreshing" because most writers are quietly ashamed of the persistence with which the movies have struggled to present authors as heroes. Insecure in life, alcoholic and disastrous at nearly every decision, as weak as wet tissue paper, Scott Fitzgerald still ended up as Gregory Peck in an awful movie called Beloved Infidel. The robustly cruel, selfish and lying Hemingway might have smiled to see George C Scott's rugged, noble veteran in Islands in the Stream. In Julia, it was heart-warming to have Jane Fonda (so much prettier than Lillian Hellman) and Jason Robards (so much more independent than the real Dashiell Hammett), seeming to suggest that no kid could have dreamed of more honest, gutsy, reliable parents.

I was about to search around for the film in which someone had played William Faulkner - but no, I couldn't quite summon that one up, in part because Faulkner's prose is still as dark, visceral and infernal as America and also because the sage of Yoknapatawpha County was actually an unyielding racist until the end of his days (1962) in Oxford, Mississippi. He may have been a genius and a Nobel Prize winner as well as a handsome little dandy with silver hair and moustache. But he wasn't house-trained or politically correct.

Moreover, as a writer, he was guilty of that criminal style that affects masters and hacks alike: he viewed and used real life and its wretched denizens as material for his words. He may have moved readers to depths of insight with his human feeling, but he shrugged it off himself. In Capote, this contradiction inspires one of the great ironies in modern film: that Capote's attention brings fresh legal aid and prolonged appeals to the two drifters who killed the Clutters, whereas Truman simply wants them executed and out of the way so that he can publish his damn book. And a fine, damn book it is.

Capotewants to suggest that Truman was so horrified by his own treachery towards the Holcomb killers that he never recovered. I wonder if he ever noticed. He lived on, a gratified celebrity, and there were others he would betray before he slept. You see, writers have a lot of nerve: they assume that life has been put there and arranged for their efforts - and it had better shape up, or watch out if the author doesn't put his knife in you. Writing has always required sharp instruments and the black blood called ink.

d.thomson@independent.co.uk

'Capote' is out on 24 February