In addition to information about individual writers and works, Murphy supplies short studies of various subgenres, including cat mysteries, gay mysteries, celebrity mysteries and more. He also features items on famous criminal cases in history, slang that's familiar from these stories and distinctive plot devices. But these are the quibbles of somebody who observes crime fiction for a living. This book is meant to be browsed and read for pleasure, not just to look up a date. There's also an entry on ricin, the poison used in the umbrella case - so the book leads you from one related topic to another.
Criticism is a dialogue, after all.
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