A sustained exploration of that odd concept ""life-style."" A witty game of musical beds with supernatural intervention. A prolonged illustrated discussion of aesthetic principles and their limitations. An investigation of will and causality. The vehicle of all these ambitions is a stylized narrative of an epic feud on a terra-formed Mars some thirteen centuries hence, accompanied by a series of complex literary parallels and allusions (from Homer and Ovid to Thoreau and The Tale of Genji). The planet itself is a bizarre cornucopia of Terran and artificially mutated species. Through an omniscient memory-bank known as ""the Vision,"" its citizens have computerized personal access to virtually the sum of existence in all space-time. What to do with these as-good-as-infinite possibilities is the sole concern of Turner's Martian society, which maintains a strict system of castes based upon aesthetic superiority. One protagonist, Michael, belongs to a bullet-biting school, which eschews the Vision or any other artificial enhancement of reality. He is challenged to a ""status-war"" by the beautiful hermaphrodite Narcissus, a hedonistic life-artist of the outrageous. All this might be little more than an exercise in misguided epistemology were it not for Turner's genuine powers of invention. His Mars--lesser gravity, winged flight, supplementary light-source (hence the ""double shadow"" of the title), idyllic archipelagoes, and all--is imagined with a joy, consistency, and clarity that put to shame words like ""exhilarating."" It is true that considerable chunks of this peculiar book are fidgety and precious. But why look a gift horse in the mouth? Not to be missed.