(FORTUNE Magazine) – An American mania for mystery is most conspicuous these days in the solve-it- yourself whodunits staged everywhere from hotels and cruise ships to corporate meetings. But it's the printed page that gave life to these intriguing exercises in detection. And books that dwell upon crime -- detective, spy, and suspense stories -- have ranked at the top of the fiction market in the past two years. Bookshops devoted only to mysteries have sprung up in a dozen American cities over the past decade. % Some of the biggest fans are business executives seeking challenge and surprise in a form that is not overly taxing. ''I work 18-hour days,'' says Robert Lee Morris, 39, a Manhattan designer and manufacturer of jewelry. ''If I get a chance to relax, my reading has to be escapist, thrilling. It can't be something that makes me work through the book.'' While Morris has long been an enthusiast of horror and espionage tales, he is now getting to know Spenser, the Boston private eye who appears in a dozen novels by Robert Parker and has been adapted to TV. A particular pleasure of the detective story is that it examines motives, solves a problem, and comes down satisfyingly on the side of order. ''So much of what I do in business is process -- things never end,'' says Betty Francis, 39, controller and vice president of the Boston Five Cent Savings Bank. ''But a mystery has pace, a puzzle with a resolution, and a strong closure.'' Many mystery buffs are voracious readers. Freda McCullough, 40, works in front of a Quotron at her own New York firm trading stocks for options dealers. To unwind she reads a mystery a night. On a recent Saturday she wrote a check for $1,125 to the Mysterious Bookshop and emerged with 67 new hard- cover traditional English mysteries and American detective novels. They should carry her through Christmas. Classic mysteries fall into two categories. The English ''cozy,'' in the tradition of Agatha Christie, takes place in a decorous setting and leans heavily on plot. It usually opens with a murder, points to an obvious but innocent suspect, and spins a web of clues; ultimately the crime is solved, often by an outsider rather than the police. The hard-boiled American detective story pioneered by Dashiell Hammett and Raymond Chandler relies more on characterization, setting, and realistic dialogue. Many of today's crime writers probe far beyond whodunit, folding in sociological and psychological elements from modern life: the female detective, government corruption, child abuse. Their fans look for more than plot. ''Solving a puzzle is not necessarily what interests me,'' says Richard Wilson, 55, senior vice president of Standard Oil Production Co. in Houston. He devoured Hammett and Chandler as a Los Angeles teenager and likes the contemporary writers who reflect the hard-boiled tradition. Wilson's current favorites: Robert Parker; Ross Thomas, author of the award-winning Briarpatch; and Elmore Leonard, who made the 1984 best-seller list with Glitz, about a psychopath who kills women. These contemporary books are too hard-boiled for some. ''Modern writers put in too damned much sex and gore,'' says Samuel N. Greenspoon, 66, a partner in a New York law firm. Greenspoon, who developed his taste for mysteries as an infantryman in World War II, owns over 3,000 first editions published between 1900 and 1950. Most are from the Golden Age between the two World Wars, so called because so many writers from that era have remained popular -- among them John Dickson Carr, Ngaio Marsh, and Dorothy Sayers. For ardent collectors, tracking down books is as challenging as tracking down murderers. Wilson relied heavily on trading to build his 5,000-volume library of first editions. He exchanged a good collection of modern general fiction for mysteries from dealers. Working in England for Exxon in the mid- 1970s, he picked up a collection of George Orwell first editions, including two copies of 1984. Back home he kept them until 1983, when their value was at a peak; then he traded the collection for two Hammett first editions. He paid two or three pounds each for mysteries by Dick Francis, the ex-jockey who writes about the track; some are now worth 100 times as much. Enthusiasts seeking guidance turn to a variety of publications, two of them the creations of Allen J. Hubin, 50, a mystery buff who is a human resources manager at 3M in St. Paul, Minnesota. Hubin's ''addiction,'' as he calls it, began at age 10, when he read all of the Sherlock Holmes stories. In 1967 he put out the first mystery fan magazine, The Armchair Detective, 30 pages of reviews, articles, and news. Hubin has since bowed out; the magazine is now a glossy quarterly published by the Mysterious Press in New York and the leading fan publication. Hubin's bibliography of 60,000 titles, published in 1984 as Crime Fiction 1749-1980 (New York; Garland, $91), is the authoritative work for serious specialists. He is now updating it through 1985. Another tome helpful to literary gumshoes includes biographies of authors: Twentieth Century Crime and Mystery Writers, 2nd edition (1985), edited by John M. Reilly (New York; St. Martin's, $69.95.) Literary societies of a mysterious vein suck in fans for fun and edification. The Mystery Writers of America (212-255-7005) welcomes nonwriters too, as affiliates. At meetings of the eight regional chapters, they can meet authors and hear experts on mystery or crime. Mystery Readers of America, an - unrelated organization of fans and professionals, publishes a quarterly packed with articles, reviews, calendars, and sources (MRA, P.O. Box 8116, Berkeley, California 94707). The famous Baker Street Irregulars unites the most passionate Sherlock Holmes buffs. Founded in the U.S. by writer Christopher Morley in 1934, it is named after urchins in Holmes's neighborhood who fed him information. Members slyly perpetuate the legend that Sherlock Holmes is not a legend, but lives -- as they point out, no obituary has ever appeared in the London Times. In keeping with Victorian convention, women Sherlockians have a separate organization: the Adventuresses of Sherlock Holmes. Both groups admit members who have made major contributions to Sherlockian affairs. Harold Niver, 47, owner of Sherlock's Music Co. in Hartford, Connecticut, who has assembled a collection of 4,000 items from first editions to pipes carved in Holmes's image, was elected to the Irregulars for founding a local offshoot called a scion. Sherlockians of either sex can join one or more of 184 scions; for information write Peter Blau, 3900 Tunlaw Road N.W., No. 119, Washington, D.C. 20007. The Wolfe Pack lures admirers of Rex Stout's 286-pound horticulturalist and gourmet detective to a December Black Orchid Banquet in New York and other culinary events with such dishes from the Nero Wolfe Cookbook as Duck Mr. Richards and Capon Souvaroff. Mystery fans of every persuasion meet at the annual Bouchercon, named for the late Anthony Boucher, a New York Times reviewer of crime fiction. Authors, booksellers, and hundreds of readers spend two days listening to experts on such topics as the economics of starting a bookstore and how authors put ordinary people into extraordinary situations. Or they can slip into a dark room and view scary old movies.