Law professor in Scotland is the publishing sensation of America with his tales about a female sleuth in Botswana

You could be forgiven if his name does not mean a great deal to you. Alexander McCall Smith is a hard-working university academic, serves dutifully on three ethics quangos and plays the bassoon (badly, he says). But as soon as he leaves his Edinburgh home and flies abroad, McCall Smith, 55, ceases being an anonymous law professor and metamorphoses into one of the most incredible publishing successes of the decade.

The law professor is also a part-time novelist. In America, his book, The No. 1 Ladies' Detective Agency, originally published here with a print run of 2,000, has sold more than a million copies in nine months. Soon it will be made into a television series, produced by Anthony Minghella, director of The English Patient. Internationally, it has been translated into 17 foreign languages.

So take it as read that before the year is out you will have heard a lot more of McCall Smith and his female detective Precious Ramotswe, whom The New York Times has labelled "the Miss Marple of Botswana". Professor McCall Smith says: "It is very overwhelming really." With the understatement of a lifelong academic, he adds: "It is somewhat surprising."

The book was published in 1998, by "a small publisher, on a very small scale". The professor says: "They really pushed the boat out and issued about 2,000."

Encouraging reviews persuaded the publisher to invest in a few more copies. But sales, though still in the low thousands, were enough to encourage his local publisher, Polygon, to strike a small-scale deal with Columbia University Press, which placed the books in a few independent bookshops in New York and Boston.

The shops knew they had a promising book on their hands, and promoted it until word of mouth ensured that it became a local bestseller. At this point the big publishers in New York got wind of Professor McCall Smith and his book. So in July last year, he was flown over for a meeting.

He says: "I realised something dramatic was about to happen when I went to see Random House and was given the most tremendously warm welcome. About 20 senior executives took me out for a lunch (I thought lunch had been abolished in New York) and I realised something really big was happening." It was. A big deal was signed and the novel was published. Then the effect of the reviews kicked in. "One of the most entrancing literary treats of many a year ... a tapestry of extraordinary nuance and richness," The Wall Street Journal said. The Los Angeles Times said the book had "the power to amuse or shock or touch the heart, sometimes all at once".

The book immediately flew into the top-10 lists. Last week, according to The New York Times, it was the eighth bestselling paperback in America.

The No. 1 Ladies' Detective Agency and its sequels - Tears of the Giraffe, Morality for Beautiful Girls, The Kalahari Typing Schools for Men and The Full Cupboard of Life - are unapologetically uplifting tales of Botswana's first and only female sleuth.

Precious Ramotswe is a folksy, plumpish woman who has sold her late father's cattle to set up a high-street agency to "help people with their lives". Her weapons are logic, eccentricity and wisdom. There is not a hint of cynicism in the stories, something that is central to their success, the author says.

"There is nothing in these books to offend people. My books are positive and affirmative, and people want to believe in them. I don't like the aggressive, amoral nature of a lot of contemporary writing, the sense that we should be shocking and distressing readers all the time."

Professor McCall Smith, who fell in love with Botswana two decades ago when he set up a university law school there, says: "I also show a side of Africa that has been frequently ignored. We do not really get a true picture of Africa. All we are accustomed to seeing are civil wars and starvation. These are sometimes there, but there is another very strong element, that of an incredible human decency. The characters in my books are people trying to lead decent lives in often difficult circumstances.

"These are not fairy stories. They are about qualities that exist in people. Brick by brick, the people of Botswana have built up a country they can feel proud of."

Professor McCall Smith is just back from a coast-to-coast book signing tour of the United States, where female fans were often moved to tears and he discovered, rather to his bemusement, that the Defence Secretary, Donald Rumsfeld, and his wife were fans.

Back home, the professor has signed a deal with Abacus, an imprint of Time Warner, to publish his titles in paperback, though has left the hardback rights with his original publisher Polygon, as a mark of his gratitude for the faith they showed in him when he was an unknown. In the 11 days since the paperback was published, The No. 1 Ladies' Detective Agency has sold 65,000 copies.

So will the part-time job - and the seven-figure bonanza it is offering - mean an end to his career as a university teacher? "It sounds pretty corny but I do not want to change things. I very much want to continue with what I am doing. I have managed to arrange things so that the writing does not affect my work. It really is done in my spare time," the professor says.

"The writing obviously is lucrative but I much enjoy my job. I enjoy being with my students. But I cannot fit much more on my plate and I will have to have a look at what I am doing. I do not want to make a decision just yet. What will go? My blood pressure probably."

He may have to relinquish his ethics committee duties or his bassoon-playing duties with the Really Terrible Orchestra, which he co-founded. "I play the bassoon, but not the entire instrument, as I dislike the very high notes and stop at the high D, which I think is quite high enough."

The choices at present are not too painful. He is wondering how to juggle the invitations that keep rolling in. The other day, he received a letter from the Palm Beach Literary Society. "I called my agent in New York, who said there were three things I needed to know. Number one, they're rich; number two, it's warm over there; and number three, you're going."

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