A mystery, according to Webster's New World Dictionary, is any event that remains so secret or obscure as to excite curiosity. A murder mystery is a novel, story, or play containing such an event and the gradual discovery of who committed it. The dictionary specifies murder mystery because this fiction deals with crime. Murder, as a crime, is in a class by itself. There is no way to make complete restitution to a person who is murdered, because a life cannot be given back. Seeing that the perpetrator of the crime is identified correctly, and in some way punished severely is the outcome that provides some satisfaction. Of all outlawed acts, a murder is most often the crime that initiates the action of a mystery.
In the early days of mysteries, a popular form was the short tale published in magazines. Short, and short short mystery stories are published in magazines today, and yearly there are books that contain collections of such tales. Mysteries are staged as plays, and more often are produced as movies and television shows. The most popular form of the modern murder mystery, however, is the novel. On newsstands in airports, in bookstores and shops of many kinds mystery novels fill long shelves. In public libraries patrons may see books with blue stickers on their spines depicting the profile of a man wearing a hat with a brim and smoking a pipe. Sherlock Holmes, the most widely recognized detective of all, and the world's most famous literary character, identifies the mystery section. Patrons today can choose from mysteries set in places around the world, with characters of many ages, backgrounds and capabilities. They may enjoy reading about the English countryside or the dark streets of tough areas in American cities. For variety, they can read about murder in varied time periods, and with characters who come from different backgrounds.
Despite the incredible variety of mysteries, experienced readers know that there are similarities in the storytelling that identify novels as belonging to the genre and thus deserve their blue stickers. Two main subgenres are the cozy, or the intimate, set in a country home type and the American PI, set in the mean streets of tough neighborhoods. However, no matter how cozy the English country house in an Agatha Christie novel is, or how grim the street scene in a Raymond Chandler novel may be, the basic elements of the mystery are identifiable. The characters and the surroundings are introduced quickly, a crime occurs, usually murder. Someone is responsible. At this point, the game is on. Someone takes the challenge, confronts the puzzling situation, and works to detect who is guilty. More than one person is suspect, other crimes may occur, the detective may face danger. Once the criminal is identified, the detective must explain who did it to the satisfaction of the characters in the book and to the reader.
The variety in the modern mystery of settings, themes, characters, detectives is evident in Mike Ashley's 777 page The Mammoth Encylopedia of Modern Crime Fiction (2002). In his preface Ashley states "crime fiction, as a genre, generally outsells every other field". He limits his coverage to modern crime fiction about the breaking and enforcement of the law. This excludes worlds that are primarily espionage, science fiction, or fiction depending on supernatural events or books that are called simply "thrillers". He left out two to three times the number of authors he included, having examined some 10,000 books. He identifies categories and gives examples of each.
He begins with the PI or private detective, then he describes the police procedural novels with their attention to detail. Today, with specialization being a way of life, he lists categories of detectives who are specialists in a field: legal, academic, ecclesiastic, journalistic, business and finance, sports, stage and screen. Settings for mysteries also provide categories, as the courts, historical periods, distinctive urban areas such as inner cities, ethnic neighborhoods, and urban crime scenes. The fun and games category recognizes mystery writers who do parodies, write "tongue-in-cheek". And he finds that the traditional cozy, with its pleasant setting and humor alive and well.
This discussion will utilize Ashley's categories and his exclusions of material that is not chiefly concerned with breaking the law. Ashley, however, deals with 'modern mysteries' which he classifies as those written after WWII. He states that other writers have discussed mysteries written before that period. This discussion gets to modern writers only after looking at the evolution of the mystery story. In fact, the mystery story dates back to the 19th century. The consensus of critics is that the first mystery published was the creation of Edgar Allen Poe's Murders in the Rue Morgue (1841). Auguste Dupin, the brilliant sleuth who solves the crime that baffles everyone, explains the solution. There is little mystery about the origin of the mystery.