And all this time I remained totally unaware that I was talking to a future Publishing Phenomenon, which is what McCall Smith has, since last September, become. Not, though, in the legal fields in which he has acquired his eminence. McCall Smith has achieved sudden, unexpected fame in the US as the author of a series of charming novels about - think of something that's the opposite of medicine, law and Scotland - a woman detective in Botswana. He has made it on to all sorts of bestseller lists and attracted the kind of reviews that can only be dreamed of.

But why, of all places, Botswana? Because McCall Smith knows and loves the country. He spent his youth in Zimbabwe, went to Scotland to study law, then returned to southern Africa and became involved with the University of Botswana. He set up its law faculty and wrote what is still the leading (and indeed, the only) comprehensive work on Botswana's criminal law.

He got the idea for the books while visiting friends there. "We were going to have chicken for lunch, and there was this woman in a red dress who chased and chased the chicken and eventually caught it, and wrung its neck. I thought to myself: I would like to write about an enterprising woman like that."

His heroine, Precious Ramotswe, a woman politely described as "traditionally built", uses the proceeds of the 180 cattle left to her by her father to become the country's first woman private eye. As founder and sole proprietor of The No 1 Ladies' Detective Agency - the title of the first of four (so far) books in the series - Mma Ramotswe (the respectful way to address her) solves her clients' problems with a delightful mixture of common sense, quiet observation and womanly insight and instinct.

Many of the American reviewers, stumped as to how to describe her, went for a comparison with Agatha Christie's Miss Marple, the elderly spinster of St Mary Mead, that quintessentially cosy English village with the distressingly high murder rate.

But there are no murders in McCall Smith's books, even cosy ones. "We are not here to solve crimes," Mma Ramotswe tells a potential client indignantly. "We help people with the problems in their lives." The problems include missing children, jealous spouses, petty crookery, ostrich rustling, and beauty-contest corruption. A man who disappears in the river while being baptised is traced by Mma Ramotswe to the stomach of a crocodile; she personally has to kill the suspect beast to make sure.

Her investigations are accompanied by down-to-earth but never sentimental philosophy. Mma Ramotswe has barely travelled outside her country, yet is immensely sophisticated; she is steeped in local custom, but thoroughly modern; a funny, tough cookie possessed of great wisdom. Perhaps it is misleading to categorise the books as crime fiction; they're more about Africa than about detection. There have been discussions, too, for a TV series involving Anthony Minghella.

McCall Smith has also done well in Scotland, where the books were originally published by the small Polygon press. In a few months, I am sure, they will achieve similar acclaim when they are relaunched - or rather launched - in England, by Abacus. They have been sporadically available before, without capturing much attention in spite of positive, if few, reviews; they're now hard to find here.

The No 1 Ladies' Detective Agency series is a publishing phenomenon in another, interesting way, one that could not happen in this country. There had been a good review in the New York Times, but sales were due almost entirely to the activities of small, independent bookshops, who, through their own networks, told each other how much they and their customers had liked the books.

It's a fair bet that the majority of McCall Smith's fast-growing public started off without the faintest idea of where Botswana was. In the crime-fiction trade, it is well understood that American readers are an unadventurous lot, rarely attracted to books that are not set in the US or Britain (the preferred location seems to be a Britain of nostalgic imagination). Why, then, did they so welcome these strange tales from such a foreign country?

"These books are very non-aggressive, very gentle," says McCall Smith. "They're quiet books, there's a lot of drinking of tea. They're about good people leading good lives. I think the Americans who read them are fed up with in-your-face social realism - here's something which is much more gentle, somewhat old-fashioned. They've been going through a terrible time domestically, and my books are an antidote."

Botswana is, economically, one of the most successful countries in Africa and one of the most stable, socially and politically. It also has one of the highest incidences of HIV/Aids on the continent. But there are only a few references in McCall Smith's books to what is the country's continuing dominant tragedy.

"The Botswanans themselves don't dwell on it. They just wish to continue with their ordinary lives as best they can, and as far as possible I want to respect their wishes. They don't talk about it all the time - they're obviously sensitive about it - so there's no reason why I should," he explains. Perhaps partly because of the respect and affection he has for the country, his books have been warmly welcomed locally. He has witnessed no resentment at the fact that they were written by an outsider. "I think people in Botswana are pleased that my books paint a positive picture of their lives and portray the country as being very special. They've made a great success of their country, and the people are fed up with the constant reporting of only the problems and poverty of the continent. They welcome something which puts the positive side."

The Precious Ramotswe series was not the only secret that McCall Smith had been keeping from me. He has also, for instance, had 30 children's books published; and he is a member of one of Scotland's best-known, if not necessarily most respected orchestras, regular and popular performers at the Edinburgh fringe festival with healthy CD sales.

The Really Terrible Orchestra consists of adequate musicians who don't quite make a beautiful sound together. McCall Smith ("I'm the worst bassoonist in Scotland") plays snatches of their CD to me and cackles with laughter: "Just listen to how flat we are."

He's not a workaholic, he insists, and his wife, an Edinburgh GP, and two teenage daughters are not complaining. It helps that he can write at an impressive 1,000 words an hour "when I'm at full tilt".

I ask him a few serious questions about the dangers of the misuse of genetic information; he switches without any hesitation from light-hearted chat about Botswanan detection and bad bassoonists to discussing deep ethical issues. Clearly he has no difficulty in coping with his separate lives.

He wants to continue to do so, but will his new-found success and popularity as a novelist allow it? He's about to start a 12-city publicity tour of the US, and trips to New York are becoming increasingly frequent as publishers vie to court him and feed him at expensive restaurants. "I can't deny that my life has been turned upside down. It's been overwhelming - exciting, but very demanding. But I hope that, when it dies down, I'll be able to resume normal life." Not much chance of that, I suspect.

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