An intriguing look at ten ""controversies about real voyages and discoveries, in which a deliberate hoax is a possible explanation,"" spanning five centuries, from Sebastian Cabot's 1508 North American voyage (or maybe not) to Donald Crowhurst's fatal hoax in a 1969 round-the-world yacht race. ""Everyone can identify with a hoaxer,"" Roberts suggests, ""because each of us has had the experience of seeing a trivial lie magnify into a nightmare of deception."" And once in, there's no way out. For these hoaxers ""the decision to fake an exploratory achievement determined almost everything about the rest of their lives"": Father Louis Hennepin, who claimed to have navigated the Mississippi before LaSalle, died (wrote Francis Parkman) ""in deserved obscurity""; Sam Adams, who purported to have made the first run of the Colorado rapids, became convinced he was the victim of persecution; and Frederick Cook (a double fake--Mt. McKinley and the North Pole) ""lived the last thirty years of his life in public ignominy"" but went to his deathbed protesting his innocence. A respected climber himself, Roberts seems most at home in the two chapters devoted to mountaineering hoaxes--Cook's ""climb"" of McKinley in 1906, via a route still unclimbed today (""no hoax was ever more conclusively exposed""), and Cesare Maestri's claimed 1959 ascent of Patagonia's awesome Cerro Torte (a claim still credited by some mountaineering writers, but effectively demolished here). Good fun for exploration buffs, and entertaining enough to appeal to others.