Unsolved mysteries cast a curious spell over the human imagination. While valiant scholars explore the secrets of the universe, the waiting world cheerfully prays for their failure. Indeed, the closer science brings us to understanding stars and molecules, the more fiercely we cling to homely enigmas. We make tourist attractions of the riddles of Stonehenge and the Pyramids, the Lost Dutchman Mine of Arizona, Scotland's Loch Ness Monster. In the Pacific Northwest, natives boast of the elusive Sasquatch (Bigfoot) and, in recent years, the equally elusive D.B. Cooper.

D.B. Cooper was -- or is -- the quiet, middle-aged man in a business suit who invented the crime of airline hijacking in 1971. On a Thanksgiving eve flight from Portland, Ore., to Seattle, Northwest Orient passenger Dan Cooper politely announced he would blow up the plane with a suitcase bomb unless $200,000 and four parachutes were delivered to him in Seattle.

His demands were met. The Boeing 727 then flew back south past Portland. And, says the book, "Dan Cooper jumped out the rear-bottom exit, vanished into a densely cloudy, black, cold night, and was never seen or heard from again."

The mild-mannered man who called himself Dan Cooper -- immortalized as "D.B. Cooper" through a media error -- quickly became a legend. Police, the FBI, the military and thousands of amateur sleuths combed southwestern Washington but found no trace of Cooper or his brightly colored parachute, and years of investigation unearthed no clues to his identity.

The notion that a middle-aged businessman could step off an airliner at 10,000 feet and not only survive but also elude capture kindled the public's imagination. Across the nation, songs, T-shirts and media hype celebrated D.B. Cooper's bold escape.

Who was D.B. Cooper? Journalist Max Gunther carefully qualifies the answer in "D.B. Cooper: What Really Happened." In early 1972, when Gunther was first contacted by a man calling himself D.B. Cooper, several hoaxes had already been exposed. Gunther was naturally suspicious, and when he heard no more from "Cooper," he filed away the sparse correspondence and forgot about it. Ten years later, a woman named Clara called him and claimed to be D.B. Cooper's "woman friend." She said Cooper had died in early 1982 and that she wished to tell his story.

"Clara" remains as mysterious and elusive as Cooper himself, however, for she refused to disclose her real identity or whereabouts, communicating with Gunther only in brief telephone conversations. Except for details that jibe with FBI records, Gunther must rely solely on the circumstances and plausibility of her story -- "a story whose truth can neither be guaranteed nor denied."

Against this cautionary background, Gunther tells the D.B. Cooper story. Those who hope to find here the name, rank and serial number of the "real" D.B. Cooper will be disappointed, for Clara is deliberately vague and, perhaps, even misleading on the particulars of his life.

The man she found in her toolshed in 1971 was a former World War II combat paratrooper, college educated, who had become at middle age the archetypal man in a gray flannel suit, enslaved by an affluent, suburban life style he could never quite afford. In desperation, he simply disappeared one day, abandoning home, job, family and friends to take up a new identity elsewhere. From Connecticut, he drifted to the Pacific Coast, where he wallowed in the limbo of the menial jobs that are available to a man with no past, no references, no records of education or employment.

During this bleak period, a fortuitous encounter with sky-diving enthusiasts inspired the wild idea of hijacking an airliner. Initially indulging an idle fantasy, Cooper studied aircraft design, airspeeds, altitudes, pressurization mechanisms, sky-diving techniques, commercial air routes and boarding procedures, almost unaware that his fantasy was hardening into a meticulously detailed mission.

Woven into this biography is Clara's own story of the great adventure that fell from the sky to transform the life of a timid, lonely woman. Her discovery of Cooper, their romance and their great escape to Long Island make a compelling, poignant story.

Equally compelling is Gunther's account of the hijacking itself, the massive investigation and manhunt, and the extraordinary public reaction to D.B. Cooper's audacious crime. In the end, whether Clara's story is true or not is relatively unimportant. It's a good story, and Gunther tells it well.

"Folks are actually pulling for this man," noted a local tavern keeper during the search for D.B. Cooper. Happily, Max Gunther's fascinating book can only enhance the legend.