In 1974-75, Wade Davis and Tim Plowman traveled the length of South America, living among a dozen Indian tribes, collecting medicinal plants and searching for the origins of coca, the sacred leaf of the Andes and the notorious source of cocaine. It was a journey inspired and made possible by their Harvard mentor, Richard Evans Schultes, the most important scientific explorer in South America in this century, whose exploits rival those of Darwin and the great naturalist explorers of the Victorian age. In 1941, after having identified ololiuqui, the long-lost Aztec hallucinogen, and having collected the first specimens of teonanacatl, the sacred mushroom of Mexico, Schultes took a leave of absence from Harvard and disappeared into the Northwest Amazon of Colombia. Twelve years later, he returned from South America, having gone places no outsider had ever been, mapping uncharted rivers and living among two dozen Indian tribes. He collected some twenty thousand botanical specimens, including three hundred species new to science, and documented the invaluable knowledge of native shamans. The world's leading authority on plant hallucinogens, Schultes was for his students a living link to a distant time when the tropical rain forests stood immense, inviolable, a mantle of green stretching across entire continents. It was a world greatly changed by the time Davis and Plowman began their journey, nearly thirty years later, and changed further today.