The paperback top 10 currently features the usual stash of film tie-ins, thrillers, glossy romance, superior sci-fi. The authors are well-known: Len Deighton, Terry Pratchett, Danielle Steel. The titles are punchy and macho (The Firm) or punchy and girly (Jewels).

There is one exception, however, currently at number five and rising: on Monday, publication day, it sold 40,000. In America, it has sold 4 million hardback copies after 61 weeks in the charts. Oprah Winfrey devoted a show to it. Steven Spielberg has bought the film rights; Clint Eastwood is pencilled in to star.

And the book? The title, The Bridges of Madison County, is disastrously un-snazzy: who are the Bridges? And where is Madison County? The cover features a small, faded photograph of what looks like a barn on stilts. The all- important first line is obscure: 'There are songs that come free from the blue-eyed grass, from the dust of a thousand country roads.' And who on earth is its author, Robert James Waller?

This is how the Wall Street Journal describes him: 'Robert James Waller is 53. He stands 6ft 1in and is arrestingly thin but fit- looking. His silver hair is swept straight back from his forehead and curls over his shirt collar. He is a vegetarian who smokes cigarettes and jogs. He drinks instant coffee. He is partial to jeans, denim jackets and cowboy boots.'

Somewhat surprisingly, this man was dean of the business school at the University of Northern Iowa until December 1985. Then, according to the WSJ, he 'sort of drifted, writing essays for the Des Moines Register, playing music, taking photographs and teaching a few courses in decision-making at UNI'. In July 1990, he spent a day photographing the historic covered bridges of Madison County, south-west of Des Moines. When he got home to Cedar Falls, he decided to write a novel. He wrote for 14 days, breaking off only to eat and sleep.

His hero, Robert L Kincaid, is 52. He is tall and thin and hard. He has silver-grey hair that hangs well below his ears. He doesn't eat meat. 'Haven't for years. No big deal, I just feel better that way.' He smokes Camel cigarettes and jogs. He drinks coffee and wears faded Levi's. And yes, you guessed it, Robert Kincaid is sort of drifting. Mainly, he's a photographer who writes and plays guitar a little. Right now, he's on assignment for the National Geographic, photographing the historic, covered bridges of Madison County.

However, unlike Robert James Waller, who has been married for 31 years, Robert Kincaid is fancy free. In Madison County, he meets a 42-year-old woman of Italian origin (Francesca) whose family is out of town for a few days. As Francesca later writes to her grown-up children: 'We talked and danced by candlelight. And, yes, we made love there and in the bedroom and in the pasture grass and just about anywhere else you can think of. It was incredible, powerful, transcending (sic) lovemaking, and it went on for days, almost without stopping.'

Tragically, 'If not for your father and the two of you, I would have gone anywhere with him, instantly. He asked me to go, begged me to go. But I wouldn't, and he was too much of a sensitive and caring person to ever interfere in our lives after that.'

A lot of guff has been written about why this idiotic story is rivalling Gone With The Wind as the fave read of all time. Some commentators have gone for the 'we all yearn for transforming, impossible love' theory. (See Eric Segal's Love Story and the film, Ghost). Or there's the one about Zeitgeists: sex and shopping in the Eighties; true love and loyalty in the Nineties.

Another popular theory is that middle-aged Americans are undervalued as a demographic group, hence the success of Sleepless in Seattle (the hero is a widower, the film is a sex 'n' violence- free zone). Bridges of Madison taps into the idea that the mid-West embodies older, purer values than coastal America and, a mere 171 pages of large type, is an ideal length for an exhausted mum . . .

At last, somebody gets the point: The Bridges of Madison County is a woman's book, and a book for everywoman, not only oppressed, working-class housewives. Francesca is a shadowy figure. We know that her nipples are clearly outlined when Robert (sorry, Robert Kincaid) photographs her in a T-shirt. But otherwise, 'She was lovely, or had been at one time, or could be again.' No unfeasibly long blonde hair, or oversized breasts that might prevent the reader identifying with the object of Robert Kincaid's desire.

Robert Kincaid, by contrast, gets acres of description. He is hard and muscular and knows all about complicated camera equipment. One time he bought a motorcycle in San Francisco, ran it south to Big Sur and made love on the beach with a cellist from Carmel. He lights his cigarettes with a Zippo lighter. In other words, your basic Hemingway package.

But there's more to Robert Kincaid than fuck 'em and chuck 'em. He dreams about owning a golden retriever. He smiles softly. He writes poems, butch poems, with titles like Too Close to the Fire. Most importantly, he finds 'most young women unattractive, regardless of their exterior beauty. They had not lived long enough or hard enough to possess those qualities that interested him.' Great: female readers can fill in the blanks.

True, the book is full of cliches. And it's impossible to understand why Francesca decides to stick it out with boring hubby. But Robert Kincaid is a new archetype: he's not the last of the cowboys, as the author keeps telling us, but an Iron John for girls, a literary Sam Shepard who fulfils the impossible demands made by the modern woman. He is, 'A graceful, hard, male animal who did nothing overtly to dominate her, yet dominated her completely, in the exact way she wanted that to happen at this moment.'

The astonishing thing about Robert Kincaid is that his progenitor is a man, a species widely believed to have no idea what women want.

Perhaps the one woman who isn't seduced by Robert Kincaid is Caroline Upcher, the freelance editor who bought UK rights to the book two years ago, before it had been published in America, for a canny pounds 11,000. Less cleverly, she changed the title to Love in Black and White and it sold a modest 2,500 when it was published by Sinclair-Stevenson in summer 1992. Since then, of course, the book has become a fully fledged Phenomenon - hence the paperback clone of the American edition published here this week. And Robert James Waller? The franchise looks set to continue. His next novel, Slow Waltz at Cedar Bend, is about a maverick, middle-aged academic (remember that teaching job at UNI?), a woman and a 'haunting and poignant story of a once-in-a-lifetime love' . . .