John Dickson Carr was one of the most prolific and popular mystery authors from the 1930s through the 1960s, writing more than 80 novels and collections of short stories, at least 200 book-review columns for Ellery Queen's Mystery Magazine, and numerous radio scripts for the BBC and CBS. Carr's specialty was the locked-room mystery, in which a crime, usually a murder, is committed under circumstances that seem utterly impossible. He believed in treating the reader fairly, within the terms of the genre: the reader is supposed to be given all the clues needed for the solution, and no supernatural or other devices are to be used. He despised the hard-boiled urban mystery, but in outlook and temperament, he greatly resembles an author whose work he hated, Raymond Chandler. Greene spends much more time in describing Carr's stories than in describing his life; Carr's alcoholism is dismissed in a few pages, and the supposition that he worked for British intelligence before and during World War II is relegated to an appendix. Despite this focus, Greene has created a solid introduction to a key figure in the history of the genre