In an African game preserve, established to protect some of the large herds of animals in the region from hunters, a gorilla attacks a native ranger who is patroling the reserve's boundaries. The attack is witnessed by Caw Caw, a crow belonging to Jungle Jim. Caw Caw picks a note from the ranger's hand and carries it to Jungle Jim, who is fishing with Skipper, a small dog, and a young chimpanzee. After reading the message, which is from Frank Bentley, warden of the Nairobi Game Preserve, Jim follows Caw Caw to the ranger's body and is surprised to see gorilla prints near it because he knows that gorillas are not native to the area. Then, on the way to the game preserve, Jim saves a young woman on horseback from another gorilla attack. She introduces herself as Nyobi and explains that she got lost while on caravan. Although Jim is skeptical of her story, he allows her to accompany him to the preserve. There, Barbara Bentley, the warden's niece, tells Jim that Bentley is ill with jungle fever. Without the knowledge of Brandt, Bentley's doctor, Jim treats the warden with a native plant, and he recovers enough to disclose that agents have been searching the preserve for gold stolen during the war by the Nazis from the country of Shalikari. Unknown to Bentley, Brandt is allied with the treasure hunters. When he returns from treating one of his cohorts, who was wounded by Jim while dressed as a gorilla, Brandt throws away the native remedy and shortly afterward, his henchman Kramer strangles Bentley. Kramer then releases a man-killing leopard from a cage and, while Jim fights it, makes good his escape. The next morning, some rangers search for the gorilla. In the secret cave, where they are digging for the hidden gold, two of Brandt's men dress in gorilla costumes and scare them off. Alerted by the natives, Jim heads toward the cave. When a lion attacks one of the supposed gorillas, Jim comes to his rescue and, in the process, learns that it is really a disguised man. The man agrees to talk, but before he can, Brandt shoots him. Later, Nyobi tells Jim that she is the princess of the country from which the gold was stolen. Brandt overhears their conversation and learns that Jim is suspicious of him. The next day, Jim, Nyobi, Barbara and Brandt search for the second gorilla man, and along the way, Brandt inadvertently reveals that he is not a zoologist as he had claimed. Nyobi and Brandt stay behind while Jim and Barbara climb the cliffs, and Nyobi is captured by the treasure hunters. Then after several attempts to scare them away, Jim and Barbara discover the secret entrance to the cave and are also taken captive. Jim manages to free himself and the women. When the rangers arrive, having been summoned by Jim, a shootout ensues, and Brandt falls to his death. Nyobi now returns home with the gold.