Lost the plot?

So, Stephen Fry has changed the ending of Evelyn Waugh's Vile Bodies soon after changing its title (to Bright Young Things). Now, instead of possibly dying on the battlefield alongside a strange girl, its hero Adam Fenwick-Symes returns safely to the arms of his sometime fiancée. The "happy ending", as Waugh ironically named his own acid finish, is now stripped of quotation marks.

"Very rum," murmurs Waugh's grandson Alexander. But Fry's no doubt honourably intended effort is far from the the most daring - or dumb - movie departure from the printed page. In an industry where its own screenplays are now treated, even by screenwriters, as rough sketches due rewrites mid-production, the visual medium's historic discomfort with words is at an all-time high. Bestselling books are bought for their built-in audiences more than even the bones of their plots. And, as explained by Adaptation, Charlie Kaufman's phantasmagoric riff on his failed effort to turn a non-fiction bestseller on an orchid expert into celluloid, sometimes translation is simply impossible. As Alexander Waugh wisely observes: "A film is a film. And a book is a book."

The most grimly funny example of how Hollywood's commercial currents can gradually wash away every good thing in a novel, without even noticing, remains The Bonfire of the Vanities (1990). Tom Wolfe's original was of course a sprawling, caustic satire on Eighties New York avarice, showing unrelieved selfishness across class and racial divides. Brian De Palma's version soon fixed that.

For Sherman McCoy, the vile yuppie "Master of the Universe", we got likeable All-American Tom Hanks. An emaciated, corrupt British tabloid hack? Bruce Willis wanted to show his range in the part. As he had none, it was changed to a smirking, loveable US lunk. The script (by Michael Christofer, who had recently remade Brief Encounter so the lovers end up together) soon let the cast be (in producer-speak) "redeemed". An ending in which Hanks saves the day by fighting off his enemies with the courtroom's sword of justice, and the black hit-and-run victim he abandoned to die gets up from his hospital bed and walks, was reluctantly discarded by De Palma just before release. A classic example of a book bought and made for "prestige" that no one involved understood, it was a legendary flop.

Such Hollywood eviscerations are nothing new. Howard Hawks's To Have and Have Not (1945) deliberately gutted Hemingway's book, transposing it from Thirties Florida to Forties Vichy French territory to ensure it was more like Casablanca, and making Bogie and Bacall's screen meeting the point. Hawks's one-liner for a glowing Bacall - "you know how to whistle, don't you?" - immediately out-stripped Hemingway's entire book in public affection. John Osbourne's 1963 screenplay shamelessly turning Henry Fielding's 1,000-page Tom Jones into a quick-fire bawdy romp with a sexy eating scene similarly cut to the chase.

More frustrating, though, was Sam Peckinpah's 1972 cutting of pulp great Jim Thompson's finish to The Getaway. In the original, the robbers descend into a world of literal shit and doom, in a criminal purgatory run by the Satanic El Rey. For the film Peckinpah and his star Steve McQueen chose the shoot-'em-up/ happy ending option.

Bowdlerising is another occassional factor, even today. In Breakfast at Tiffany's (1961), you'd be hard-pressed to detect Audrey Hepburn's achingly glamorous character is, as per Truman Capote, a prostitute. Readers of Brett Easton Ellis's American Psycho watching the 2000 film, meanwhile, steeled themselves needlessly for most the awful and powerful scene, combining prostitutes, their vaginas and caged rats; like most of the book's savagery, it remains unfilmable.

Some authors simply snap at sacrilege to their texts - Theodore Dreiser was the first to sue a studio, in 1931, for changing his An American Tragedy into "a Mexican comedy". Nine years later, though, poor and sick, he was offering to give his masterpiece Sister Carrie "a somewhat more optimistic ending - several of which I have in mind". John Irving, not so cash-strapped, forced an adaptation of his A Prayer for Owen Meany to change its name to Simon Birch (1998), so far had it strayed.

That said, every now and again an adaptation does work. David Cronenberg made an honest stab at William Burroughs's smack-flattened, plot-free cut-up Naked Lunch - by delving under the words, to show the parts of Burroughs's Casbah life they encoded. Similarly, Apocalypse Now's radical removal of Joseph Conrad's Heart of Darkness to the Vietnamese jungle, remained faithful to an author's spirit. "The horror, the horror..." was present in Brando's blackened face as much as Conrad's Congo. In general, though, failure is the rule.

The comic-book is perhaps the only (semi-)literary form Hollywood has shown recent respect for. But October's The League of Extraordinary Gentlemen lets even this visual zone down. Alan Moore's comic's sly filleting of Victorian fiction brought together characters like Nemo and Allan Quatermain, under the leadership of self-proclaimed vampire Mina Harker, in a richly literate adventure. The movie adds a token American (Tom Sawyer), forces the female character to the sidelines, replaces Moore's resonant plot with random action scenes, and inexplicably destroys everything of value in its source. Compared with Moore, Wolfe and the rest, Waugh can rest easy.