Planning to make an expedition into the Matto Grosso jungle, George Breakston and Yorke Coplen fly from Los Angeles to Brazil. Their Brazilian guide is explorer Mike Roginsky. Accompanied by Brazilian natives, Breakston and Coplen search for an English explorer who disappeared in the jungle twenty-five years earlier and is now rumored to be the leader of a group of Indians. Along the way, Coplen wrestles with an alligator. On the river, a native falls into the water and is eaten alive by piranhas. The expedition arrives at a small village, where they meet a white doctor. Although he has no information about the lost explorer, he tells them about a white woman who has been captured by a band of Urubu Indians. Led by the doctor, they rescue the woman, a schoolteacher. When the men are about to leave, they discover the body of a white man dressed in Indian garb. Because he is dead, however, Breakston and Coplen realize they will never know if he is the man for whom they were searching.