In the African jungle, a white missionary and a village chief named Mahala, who has just arrived from abroad, where he was studying, ask Jungle Jim to track down a mysterious white woman, who lives alone in the jungle with a tiger. The woman has been responsible for attacks on the witchmen of the tribe, particularly Hakim, the chief medicine man. The missionary speculates that the woman might be the grown child of Mr. and Mrs. John Martindale, archeologists who were murdered while searching for the ancient sacrificial lake of the witch doctors known as the Lagoon of the Dead. Hakim, who has been acting as the chief during Mahala's absence, is not pleased to learn that he is returning. Before Jim and Mahala reach the village, some of Hakim's men start a rock slide, intending to kill them, but Jim and Mahala escape with minor injuries. Mahala's people welcome him back and report that Hakim is hunting for the white woman, whom he has vowed to kill. Jim then decides to find her before Hakim can carry out his evil plan. Before he finds the mysterious woman, Jim encounters Barton, a treasure hunter who is seeking the Lagoon of the Dead, where he hopes to find gold and jade sacrificial relics. Later, Jim kills a crocodile that attacks him and foils several of Hakim's murder attempts. Eventually, Jim and Mahala trail the woman to a cave that is hidden behind a waterfall. There they discover photographs of the Martindales, confirming the theory that she is their daughter, Joan. They also find a letter revealing that Hakim intended to sacrifice the Martindales. Barton joins them in the cave, and they all follow a hidden passage to the lagoon. While Barton and his men dive for treasure, Jim rescues Joan from quicksand. Meanwhile, Hakim discovers Barton at the Lagoon of the Dead, and Barton exhorts him to kill Joan, the only witness to her parents' murder, as well as Jim and Mahala. After Jim is knocked unconscious when he falls off a cliff, Hakim leaves him for dead and brings Joan and Mahala to the lagoon, intending to sacrifice them. In the meantime, Jim regains consciousness and rouses the jungle animals. Barton and Hakim are killed during the ensuing struggle, and Mahala returns to his village with the treasure, which will be used to benefit everyone.
