It started when John Berendt wrote a book about the Deep South town, its residents and its dark secrets. Then the film rights were sold and life changed for ever. Lucy Broadbent on how the populace is starring in its own true-to-life movie.

There is a wait of at least an hour to get breakfast at Clary's Drugstore in Savannah these days. There are crowds of tourists in the leafy Monterey Square outside Mercer House, it is almost impossible to get into Lady Chablis' nightclub and Emma's Piano Bar is packed every night.

John Berendt had never intended to transform the lives of the residents of Savannah quite so radically when he wrote his book about them. He never anticipated that its success would turn several of them into movie-stars, make half the town celebrities and provoke one of the greatest pilgrimages to America's Deep South since Gone with the Wind.

But then Midnight in the Garden of Good and Evil was not an obvious candidate for mainstream success. The true story, about an antique dealer accused of shooting and killing his much younger lover, was at first deemed to be too obscure.

But four years after it first appeared in bookshops, Midnight, the book has become Midnight, the phenomenon, taking up long-term residence on bestseller lists the world over. It is now published in more than 21 languages.

More impressive than the book's sales figures are the numbers of tourists to Savannah, where the mystery takes place. Already the number of visitors has doubled; so has the revenue to the city - and the film is not even out yet.

Now, however, Clint Eastwood's much-anticipated portrayal of events which he directs on film has opened in America, and Savannah's residents are bracing themselves. Just as the beautiful flatlands of Madison County in Nebraska became a major tourist draw after Clint Eastwood directed and starred in The Bridges of Madison County, so too is Savannah in Georgia.

"I don't have anything against tourists," explains Luther Driggers, the town's inventor, who is immortalised in the book and probably the only person in town who declined to have lunch with Clint Eastwood. "But they're everywhere, they're in the way. And if you think it's bad now, these people are the literate ones. Wait till the movie comes out."

Not everyone is so displeased by the book's runaway success. John Berendt made one stipulation when he sold the movie rights to his book: that all the real people he mentioned be allowed to audition for their characters. As a result Lady Chablis, a flamboyant drag queen whose performances in a local nightclub are a major feature of the book, has become the star she always wanted to be. There are others too, like Emma Kelly, the town's acclaimed piano player, and Jerry Spence, the hairstylist.

But nobody was more prepared for fame than Chablis. She has already published an autobiography, called Hiding My Candy, for which she earned a $100,000 advance. "Honey, I've been living like a movie star all my life. Now I'm going to be one," says Chablis, 40, who insists she lives life as a "she", not a "he".

She says she is loving the exposure, but had only one complaint about the filming. "They put me up at the Holiday Inn. So I told Clint. "Y'all forgot. I am the Doll. I do not stay at the Holiday Inn.' There was not enough room there for my luggage. And Clint apologised. He said, `I can't believe they did that to you, Doll'. He was so wonderful."

The film tells the story of Jim Williams, who was renowned as a wealthy antiques dealer and restorer of fine homes in Savannah. His reputation as a collector was widespread enough to persuade Jacqueline Onassis to visit his extraordinary home, Mercer House, in the Seventies. Invitations to Williams' Christmas parties were prized among social climbers.

Then, on 2 May 1991, an argument began in Mercer House between Williams and Danny Hansford, a teenage street hustler with a volatile temperament whom Williams had taken in both as an employee and as his lover.

Williams always claimed that he shot Hansford in self-defence, after he attacked him. But he was tried four times for first-degree murder before he was finally acquitted in May 1989. Whether he did or didn't murder him remains one of Savannah's many dark secrets. He died a few months later of heart failure.

"Williams liked the idea of someone writing a book about him," says Berendt, 50, who lived in Savannah for eight years. "I seemed willing to listen to his side of the story." Berendt never includes his own opinion on whether he murdered Hansford or not, and leaves the reader to judge.

While the book follows Williams' story, it also details the lives of a menagerie of characters living in the town. Kevin Spacey is to play Williams, John Cusack plays Berendt, Eastwood's own daughter, Alison, also has a part.

Most extraordinary of all is Eastwood's unprecedented decision to cast hundreds of local residents. Jim William's sister, who now owns Mercer House, permitted Eastwood to film some scenes in the actual rooms where the events occurred. The problem with that was that when it came to the Christmas party scenes, the house contained so many valuable pieces of art and furniture that it presented a security problem. Eastwood decided, therefore, not to use extras. But to send out engraved invitations to the same high society Savannahians that Williams' always used to invite to his parties, and the result is real life partying on film just as it would have been in Williams' day.

Across town, the impact of the book is ever-present. There are Midnight- inspired maps of Savannah, T-shirts, and even photocopies of Jim William's last will and testament on sale everywhere. In April 1986, the mayor pronounced there was to be a John Berendt Day and temporarily renamed Monterey Square after him. Clint Eastwood has made his own contribution, a donation to the Lucas theatre.

"The city hasn't lost its sense of self," says Berendt, who is now researching another book in Italy. "But there is a feeling now that the world is looking at it. And I don't know what impact it will have over the long term."