In the nightmarish last days of the Third Reich, a psychotic Nazi scientist (Robert Vaughn) escapes to the impenetrable jungles of the Amazon rainforest. Years later, a mysterious incurable disease breaks out among the natives and adventurer John Hamilton (Michael Dudikoff) is hired to lead investigators on a search for the cause. Braving bloodthirsty river pirates, hostile native tribes and headhunting cannibals, Hamilton, guides a group of explorers up the deadly Rio del Morte to the fabulous lost Inca city.