Doug Cassidy is a university professor of archeology specializing in the Inca of Peru. In this third book of the trilogy, Doug and his wife Emily Howell travel with an expert team of scientists to Tiahuanacu in northern Bolivia just south of the famed Lake Titicaca, the world's highest commercially navigable lake. Their mission is to discover the origins and meanings of a large solid-rock gate and the calendar that yet today still exits near its top reaches. This is, after all, the place where the Inca supposedly originated. What Doug and his group find, however, is more than they bargained for. Abundant radioactivity, groups willing to sacrifice everything to keep that radioactivity secret, and an earth-shaking discovery that will, if true, rewrite the origins of intelligent life on earth.