The case of the reappearing crime novel: readers curl up with a good `whydunit'. Crime does pay. That's what some long-suffering mystery writers are discovering, as the genre emerges from the shadows of popular literature (right). Meanwhile, women in these books, and the women who write them, get aid from a group called Sisters in Crime (Page 18)

WHEN Otto Penzler opened his Mysterious Bookshop in Manhattan 10 years ago, people ``would wander in off the street, look down their noses, and say they never read mysteries. Now when they come in and say they haven't read any, they look abashed.'' Mr. Penzler, owner of Mysterious Press, a publishing company devoted to mysteries, calls this the ``Second Golden Age'' of crime fiction, similar to the 1920s and '30s. Crime writers, once considered a bit disdainfully as ``genre'' writers, are now getting mainstream contracts and making the best-seller lists. Mainstream writers are crossing over into mysteries. Mystery bookstores (perhaps 50 of them) are strewn around the country like bodies in an Agatha Christie novel.

While figures on crime fiction sales are elusive (publishers don't break down fiction into categories), industry sources confirm the growth.

``There are definitely more books being published,'' says Susanne Kirk, executive editor at Charles Scribner's Sons. ``The Book-of-the-Month Club started the Mysterious Book Club, and [paperback publishers] Pocket and Bantam are now putting out mysteries in hard cover.''

Why is this genre, whose books have been quietly inhaled by armchair sleuths for a century, suddenly so popular?

Some people in publishing say one reason is that it's one type of fiction that still has structure and strong storytelling.

``People are on the rebound from modern fiction,'' says mystery writer Rick Boyer, who has strolled into Spenser's Mystery Bookshop in Boston to autograph copies of his new book, `The Whale's Footprints.' ``Narrative has become less and less important. Mystery novels are strong on plot, and necessarily so. The best storytelling is in crime fiction, in terms of rising action, falling action, and suspense. Things happen in these books.''

``What's happening is, a lot of writers look at mainstream novels and see what's getting published is this minimalist stuff, beautifully written stuff about the boring lives of boring people; they want to tell a story about interesting people,'' says Tony Hillerman, president of the Mystery Writers of America, who has written 16 books, nine of which are mysteries.

Otto Penzler reasons that the trend in crime fiction coincided with the country's trend toward conservatism. ``In murder mystery, a bad guy comes in and breaks the social fabric. The detective captures that bad guy and stops him from doing it, restoring the social fabric. That's a conservative notion.''

``Crime fiction has always been considered kind of escapist - not really good literature,'' says reviewer Jane Spitzer. ``People read [them] because of the sense of order and rationality. It's very much the forces of good versus forces of evil. There are, of course, gray areas, but in the end justice prevails.''

The genre is luring mainstream writers, says Penzler: ``Norman Mailer, Joyce Carol Oates, Mario Vargas Llosa. Even Tom Wolfe's `Bonfire of the Vanities,' that could be considered a mystery. The great trend is a blurring of the lines between mystery fiction and general fiction.''

Much of that has come from the influx of women writers, who started writing crime fiction after World War II, says B.J. Rahn, who teaches courses on British and American women crime writers at Hunter College in New York. ``By using mainstream literary techniques, they've taken it from crossword puzzle to full-fledged literary novel,'' says Professor Rahn.

``They've used setting the way mainstream novelists do to develop character, advance the action, create mood, and implement themes. And because women are interested in people and relationships, they have been pioneers in development of in-depth psychological studies. They've taken it from `whodunit' to `whydunit.'''

Readers like them because they're intellectually challenging. ``What draws me is the puzzle solving; the neatness of the solution,'' says Barbara B. Simons, a free-lance editor in Boston. ``You always know there's going to be a satisfying and neatly tied up ending.''

`The mystery has its conventions,'' said best-selling British author P.D. James in an interview on the Public Broadcasting System's ``Mystery!'' For example, she notes: ``The central mysterious death; the closed circle of suspects; the detective, either amateur or professional, who comes in to solve the crime; the solution by the end of the book which the reader should be able to arrive at himself or herself by logical deduction from the clues which the author has inserted with deceptive cunning but essential fairness.''

That's always been true of mysteries, since they began with Arthur Conan Doyle's Sherlock Holmes and Edgar Allan Poe. (Most say mystery fiction got really moving with Raymond Chandler and Dashiell Hammett in the '20s and '30s.) But crime fiction, as popular culture, reflects what's going on in the world. And that world has grown more violent.

``More mysteries are violent than before. Detectives have always acted out of a moral code,'' says Jim Huang, who works at the Spenser shop in Boston. ``The difference today is that detectives are willing to go to extreme ends to achieve results.''

This is a genre that sprawls from Agatha Christie's sedate poisonings in the English countryside to John le Carr'e's international spies, to Andrew Vachss's dark and turbulent journeys through Manhattan's Lower East Side. And it's expanding. There are Dutch and Japanese investigators. American crime writers are writing about their own regions, and giving the same kind of specific rendering of their locales that made Chandler's Los Angeles so vivid.

``There's a group of Denver PIs, some in Seattle, a whole school of Midwest PIs - more ethnic, working class,'' says Mr. Huang. ``People like reading about where they live, but the flip side is that they like to read about exotic places. Tony Hillerman opened up the Southwest.'' Mr. Hillerman writes about Indian customs in his books about a Navajo tribal policeman.

Crime fiction ``has been treated as a second-class citizen, critically, and in advertising and promotion,'' says Ms. Spitzer. ``But that's beginning to change. It's being taken seriously.''

``Mystery writers are now being talked about and reviewed and treated in college courses as major American novels,'' says Penzler.