Nor should there be. The mystery as a separate genre has been around at least since Edgar Alan Poe invented the detective story. But its ancestry goes back much further, perhaps as far back as Oedipus's saving Thebes by solving the riddle of the Sphinx. The mystery is a specific instance of the quest motif in which the hero sets out to accomplish an objective and suffers various adventures along the way. Medieval romances are classic examples of the quest motif. But the specific quest of the mystery story is for the hero or heroine to discover who committed a particular crime, usually a murder.
Authors of mysteries have a wide range of possibilities to choose from, for subgenres of the mystery vary in subject and tone from the hard-boiled police procedurals and tough private eye stories to satin-mannered "cozies" like Agatha Christie's Miss Marple series.
May I illustrate this variety of choices with a personal example? My choice for Rhapsody in Red (and its forthcoming sequel) was a kind of borderline cozy set on a contemporary college campus. One would expect colleges to provide a quiet environment protected from the riptides of the outside world. Indeed, each campus ought to be Shangri-La brought into real life. Unfortunately, colleges can become snake pits of turf wars and conflicting value systems. So my twenty years as a professor gave me a rich field of possibilities for the novel.
That said, I firmly believe the business of fiction is to entertain rather than to instruct about social, political, or philosophical problems. If a reader wants instruction, he should read nonfiction. However, fiction can illustrate particular viewpoints on serious questions. So I began planning the novel with several serious questions as well as some less serious.
Given the built-in conflicts between a college faculty and the college administration, what would happen if a professor actually said what the other professors were thinking but lacked the nerve to say? How should a college resolve such conflicts as commercialism vs. academic standards, education vs. indoctrination, and Christian orientation vs. secularism? What would happen if the political correctness diversity mania brought a Wiccan into a denominational college's Bible Department? And how would a person cope if he had a constant uncontrolled stream of music running through his head (musical hallucinations)?
Such a mixture of serious, satirical, and comic questions ought to give a novel enough substance combined with enough comic relief to keep things interesting. I hope the result proved as fruitful as the prospect appeared. Only the readers can make that judgment.
But the lighthearted narrative with serious overtones is only one of the many possibilities of the mystery genre. The genre promises something for everyone: there's the tough world of the police procedural, the violent world of serial killers, the quiet world of Miss Marple, and all points in between. That variety is the reason the mystery genre remains and will continue to remain popular.