In Talking About Detective Fiction, P.D. James, a master of the art, explores the genre's mysteries.

How do detective stories differ from crime fiction in general?

Crime fiction is a very wide spectrum of writing. You have crime at the heart of the book, but you may know who did the crime. The interest is more in whether the criminal is going to get caught and the effect of the crime on him and society. In a detective story, you have a mystery at the heart, usually a mysterious death. You have a closed circle of suspects and clues, and the detective comes in like an avenging god to put things straight. By the end of the book, the reader should be able to decide correctly who committed the crime.

Of the major golden age mystery authors, why is Agatha Christie still so popular?

The great virtue of Agatha Christie was that she was a supreme puzzler. I don't think she was a superb writer as far as style is concerned. Nearly always, her murders would not have worked in real life. But she was extremely clever at providing a mystery and puzzling us. It's as if she's placing her cards face down and we think, “Yes, that's the one,” and when she turns them up, we're always wrong.

Was classic British detective fiction always concerned with class?

In the golden age, it was rather taken for granted in the English village and everybody knew their place. One could say Dorothy L. Sayers was an intellectual snob and Ngaio Marsh was a social snob. I think it's very different now. In my own books, most of my stories go right across class. I think it's very important to have characters from all walks of life. But some people think it's a snobbish genre because, on the whole, writers find it more interesting to have a murderer who comes from a privileged background. Then you think, “What leads a man with all those privileges to cross that invisible line that divides the murderer from the rest of us?”

What role do you think television has played in keeping detective fiction popular?

Television has been incredibly powerful. On the whole, it does better with crime than it does with detection because with crime there is always something happening. With detection, a lot of it is cerebral. What television does best is to use detectives who have already become very popular in books, such as Inspector Morse. He's been extraordinarily successful on television, but most of the stories have been written for television, not by Colin Dexter. Television is important in bringing people to the books. For instance, we all know about Henning Mankell's Wallander now, which we wouldn't have if we hadn't seen him on television.