The film begins in New York City. A man buys heroin from his dealer, Mike. The man meets two mobsters who are also looking for Mike, because he owes them $100,000. The mobsters shoot the man and leave him for dead.
In Paraguay, siblings Rudy and Gloria and their friend Pat prepare for a journey into the rain forest. They plan to prove Gloria's theory that cannibalism is a myth. The trio encounter Mike and his partner Joe. Joe is badly wounded; Mike explains that they were attacked by cannibals. During the night, Gloria goes missing and Rudy finds a native village while looking for her.
Due to Joe's injuries, the travelers decide to stay in the nearly deserted village. Mike seduces the naive Pat. In a cocaine-fueled rage, he encourages Pat to kill a native girl. She is unable to do it, so Mike kills the girl himself. In his dying moments, Joe reveals that he and Mike were responsible for the cannibals' aggression. They came to the region to exploit the natives for emeralds and cocaine, taking advantage of their trust in white men. One day, while high on cocaine, Mike brutally tortured and killed their native guide in full view of the tribe. A badly charred body, previously believed to be that of a different guide, is actually this native. Mike kidnapped a native girl to lead them out of the jungle, but the outsiders were followed and attacked.
Following the latest murder, the natives hunt the outsiders. Joe dies of his wounds, and his body is found and cannibalized by the natives in full view of Rudy and Gloria, who are hiding from the natives. Mike and Pat abandon the others, but all are captured by the natives and forced into a cage. The prisoners are forced to watch Mike as he is tortured and beaten. The natives transport their prisoners to another village, but Rudy manages to escape. He is caught in a booby trap in the jungle, and his bleeding wounds attract piranhas. The natives shoot him with a poisoned dart, and he dies instantly.
Pat and Gloria are put in a hole in the ground. Mike is placed in a separate cage. A native man, whom Pat had saved from Mike's aggression, lowers a rope into the hole so the women can escape. Mike digs his way out of the cage, chases the man away and cuts the rope, preventing the women from escaping. Mike flees into the jungle, where he tries to attract the attention of a search and rescue plane, but he is recaptured. The natives sever one of his hands and drag him back to the village. The search plane lands, but the natives tell the rescuers that the outsiders' canoe capsized in the river and they were eaten by crocodiles.
After the search team leaves, Pat is bound and stripped and the natives run hooks through her breasts. Gloria is forced to watch as she slowly bleeds to death. Mike's head is locked in a crude apparatus and the top of his skull is removed so that the natives can eat his living brain. During the night, the sympathetic native returns and frees Gloria. He guides her through the jungle, but falls victim to one of the natives' booby traps. Gloria eventually encounters a pair of trappers, who take her to safety. Instead of telling the true story, she recounts the natives' lie about the others being eaten by crocodiles.
Gloria, deeply disturbed by her experiences, returns to civilization. She publishes a book titled, Cannibalism: End of a Myth, which lies to support her theory and covers up the events of her ordeal.
Who does Mike seduce?
Pat