'We lawyers get involved with people who messed up their lives, and their mistakes make fascinating stories,' he says. 'Street lawyers see the underbelly of society. Corporate lawyers see high stakes shenanigans.' This is the world inhabited by Grisham's heroes, a world where a bright young tax lawyer suddenly discovers his firm is working for the Mafia.
Enough readers have been fascinated by that world to make Grisham the leading exponent of the legal thriller, a genre that is dominating American bestseller lists. And his success has led many of America's 600,000 lawyers to dust off manuscripts and make their way to publishing houses.
But it is not just the sweet smell of success that motivates them. According to Grisham, most lawyers are unhappy, bored and looking to get out.
It was boredom which led Grisham, 39, to begin writing in 1984. He was a small-town lawyer in Southaven, Mississippi, defending people charged with assault, drug dealing and burglary. He started writing a book in long hand on yellow legal pads and took three years to finish his first manuscript. It suffered rejection by more than 30 publishers and agents before selling 5,000 copies in 1989.
His second book, The Firm, was published in 1991 and became a bestseller, enabling him to give up law and move to a 70-acre farm in Oxford, Mississippi. Within a year he became a cult figure. Late last year when Hollywood studios and production companies bid against each other for the film rights of his latest book, The Client, the winner paid a record dollars 2.5 million. It was published this year and sold 2.6 million copies in the first month.
For more than a year now it has been difficult to take a flight anywhere in the United States without seeing somebody in the departure lounge or on the plane reading one of Grisham's books. At one moment all four of his books were in the New York Times bestseller lists, and in Britain he has racked up sales of more than 500,000. The film of The Firm, starring Tom Cruise, will be released this summer, followed by films of the The Pelican Brief and The Client.
A Grisham thriller can provide a good read - what the Americans call 'mind candy'. But this does not explain the extent of his success. The rise of the legal thriller began before Grisham, with Scott Turow's Presumed Innocent in 1987, which sold 700,000 copies in hardback and 6 million in paperback. This immediately produced a host of imitators. 'Who knows how many expensive hours have been billed to unsuspecting clients by lawyers claiming they were writing briefs, when in fact they were tinkering with their novels?' Grisham says.
The success of The Firm led to a renewed frenzy. 'An epidemic of sabbaticals and leaves of absence hit law firms across the land as budding writers left their offices to finish their books,' Grisham says. 'Agents and publishers were deluged by tons of thick, unsolicited manuscripts about fearless prosecutors and Skid Row defence lawyers.'
Americans purport to hate lawyers, but the dislike is always mixed with fascination. Grisham caters for both. The runaway success of The Firm is explained in part by its anti-lawyer tone. Mitchell McDeere, brilliant but impoverished and just out of law school, is hired by a Memphis law firm for dollars 80,000 a year and a new BMW. The partners in the firm explain that no lawyer has ever left them - the main reason being, as McDeere eventually discovers, that the firm belongs to the Mafia and lawyers who want to leave die in fake accidents.
The life McDeere and his wife aspire to is very much America in the Eighties, with a high regard for people working in financial services. A security guard watching McDeere notes: 'Eighteen, 20 hours a day, six days a week. Sometimes seven. They all planned to be the world's greatest lawyer and make a million dollars overnight.'
Grisham's attitudes are more populist; he was briefly a member of the Mississippi legislature. In the introduction to A Time To Kill, his first book, he says that in 10 years as a lawyer he 'represented people, never banks or insurance companies or big corporations. I was a street lawyer'.
His books steer clear of courtroom scenes. But it was in a courtroom that Grisham got the idea for his his first novel. 'One day I stumbled upon a horrible trial in which a young girl testified against the man who brutally raped her.' This formed the basis for A Time To Kill, about a 10- year-old black girl raped by two white men in a town called Clanton in Mississippi.
It took him three years to write, getting up at 5am and working until 9am, when he started work at his legal practice. His wife Renee edited the book. Sales were disappointing but Grisham had already started The Firm, which is much more in keeping with the classic thriller formula of an ordinary individual suddenly entangled in a great conspiracy.
Both The Client and The Firm revolve around prolonged chases, which explains why they were so instantly attractive to Hollywood. Even though lawyers, judges, prosecutors, police and Mafia form the backdrop, there is very little legal detail, though plenty of attention to the lifestyle and earnings of lawyers.
All legal thriller writers emphasise how their years as a lawyer give them an insight into human actions and depravity, but the successful, such as Grisham, make sure that little of what a lawyer does professionally surfaces in their books. Certainly none of them gets bored and writes a book.