By Rebecca Jones
BBC arts correspondent
Alexander McCall Smith has written more than 50 books
Alexander McCall Smith, best-selling author of The Number One Ladies' Detective Agency, recently spoke at The Edinburgh International Book Festival about why he's trading Africa for Edinburgh, as the setting for his latest book.
The success of McCall Smith's five books about Precious Ramotswe, a plump African woman who sets up Botswana's first and only detective agency, has been nothing short of phenomenal.
The series has sold five million copies in English and been translated into thirty one languages. A sixth book, In the Company of Cheerful Ladies, is published on 23 August.
But next month there's another new book from this prolific author, called The Sunday Philosophy Club. This time it's set in Edinburgh, and features a moral philosopher and amateur sleuth Isabel Dalhousie.
"She's a bit of a Jean Brodie, but a more modern version," says Alexander McCall Smith.
"Sleuths are really very useful fictional characters because all sorts of problems can come their way. They meet all sorts of people.
"It's a literary device, which I use to explore all sorts of issues of moral obligation, the limits of moral obligation, moral problems which I think people are really very interested in in their everyday lives" explains McCall Smith.
The Sunday Philosophy Club begins with a death at the Usher Hall, a concert hall at the heart of Edinburgh's cultural life - and the city plays a central role in the book.
"Edinburgh is a marvellous character for a book," says Alexander McCall Smith. "It's such a remarkable city. It's got such atmosphere. It particularly lends itself to the haut-bourgeois noir, as opposed to other forms of noir.
"Edinburgh is a very hypocritical city. There's a veneer of politeness and underneath that, one finds an interesting story."
Alexander McCall Smith joins a long list of crime writers who've let their imaginations run riot in Scotland's capital city. Among them Ian Rankin, Quintin Jardine and Christopher Brookmyre.
Catherine Lockerbie, Director of the Edinburgh International Book Festival, says the city has always been a popular setting for crime fiction because of its split personality.
A sixth instalment of the Detective Agency series is due out this month
"Edinburgh's always had two sides, " she says. "It's had that very respectable, middle class, educated side and then a much darker side reflected in the actual physical structure of the city itself. The dark little closes of the old town.
"Think back to all the great Scottish writers, James Hogg, Robert Louis Stevenson - Jekyll and Hyde - of course it's a crime book. The city has always played host to writers, whether they have dark or slightly merrier imaginations."
As he waits for the publication of The Sunday Philosophy Club, Alexander McCall Smith must hope the public's appetite for Scottish crime fiction continues unabated. But he's not taking anything for granted.
"Let's hope that the wind is fair for the book," he says. "But one has to be careful because nemesis is always stalking around and listening to us if we make remarks of that sort."