Mysteries and their solutions have always been used in fiction, but detective fiction as a recognisable genre first appeared in the mid-nineteenth century. Despite detective fiction becoming one of the most popular of literary genres of the twentieth century, disputes over the point at which a story containing detection becomes a detective fiction story continued. In its most obvious incarnation detective fiction is to be found under the heading "Crime" in the local bookstore; it includes tales of great detectives like Holmes and Dupin, of police investigators, of private eyes, and little old ladies with a forensic sixth sense. But detective fiction can also be found disguised in respectable jackets, in the "Classic Literature" section under the names Dickens and Voltaire. Within detective fiction itself, there are many varieties of detectives and methods of detection; in its short history, the genre has shown itself to be...