An imaginative romance of shipwreck, survival, and philosophical adventuring by the formidably learned author of The Name of the Rose (1983), Foucault's Pendulum (1989), and, most recently, How to Travel with a Salmon and Other Essays (1994). In 1643, highborn Roberto della Griva, a soldier who has fought in the Thirty Years' War and subsequently been sent on a secret mission to the Antipodes, is shipwrecked in the South Pacific somewhere near the Fiji and Solomon Islands. He saves himself by clambering aboard another ship--the abandoned Daphne. Finding in its hold sufficient provisions and supplies, and gradually recovering his strength and his wits, Roberto records the events of his past life--his sheltered boyhood in Italy, confused exposure to the temporal claims of political allegiance, love of learning for its own sake, and sobering experience as devoted postulant to his scarcely approachable love objects. The tale of Roberto then is juxtaposed against his cautious exploration of the Daphne now, climaxing in the surprising fulfillment of his fears that the ""intruder"" whose companion presence he suspects may be the ""evil twin brother"" he has always had fantasies of. Simultaneously, a nameless omniscient narrator summarizes the record Roberto has left behind, ruefully assessing the latter's amazed discovery that the complexity of creation proves all things possible--including the contrary lives led by our alternative selves. Eco tests his readers severely, especially in detailed considerations of the mechanics of navigation and ""the mystery of longitude."" Yet even this novel's denser arcana are embodied in vivid characters speaking lively and funny dialogue. Prominent among Roberto's reality instructors are his genially blasphemous and metaphysically-minded father, inventor of an Aristotelian Memory Machine; his aphorism-spouting comrade-in-arms Saint-Savin; and the alarmingly polymathic scientist-priest, Father Caspar Wanderdrossel. Though weighted here and there by the longueurs of whimsy, this is on balance an intriguing and entertaining theoretical romp--a kind of Borgesian Robinson Crusoe.