In East Africa, British deputy Andrew Barnes and his assistant Eli are visited by hunter Pat Gilroy, who asks Andy to bring him to the nearest village where he can hire native guides. Their discussion is interrupted by a radio message from the Commissioner in Nairobi, informing Andy that the last hunting expedition, consisting of Professor Catesby, two Americans and Pedro Sebastian, a native guide, has been missing for days. Meanwhile, Bomba, a young white man who has been reared in the jungle, is saving Pedro's daughter Lita and her servant from a lion attack. After he wrestles the lion to the ground, Lita thanks him and explains that they are searching for her father. Bomba decides to accompany them and has his chimp friend, Kimbbo, send a message throughout the jungle asking for information. He then hears a drum message from Eli, who is also looking for more information about the missing men. Bomba drums back that he is bringing Lita to Chief Nomgola's village to look for clues, but when they reach the village, they find only the dead bodies of Professor Catesby, Nomgola and several natives. Just as the chimps return to inform Bomba that they have located the hunting party, one of the Americans, Greg, spots Bomba and Lita. After Greg grabs Lita and shoots her servant, Bomba escapes into the river. He then drums a quick S.O.S signal to Andy and Eli and follows Greg and Lita. While Eli translates the signal, Andy finds a wanted poster that reveals that Gilroy is actually notorious diamond smuggler Roy de Haven. De Haven, seeing the poster, immediately forces Andy to sail him to Nomgola, and although Andy lies to Eli that everything is fine, Eli deduces something is wrong and follows the pair. In the jungle, Bomba rescues Lita, who leads him to a nearby crater where her father recently discovered diamonds. There, they see that Greg and the other American, Hardy, have enslaved Pedro and Nomgola's tribe and are forcing them to mine the crater for diamonds. They watch as Greg returns to the site and informs Hardy that they must leave because an indestructible jungle boy is after them, but Hardy refuses to go until de Haven meets them, as planned, to help smuggle the diamonds. Although Greg guards the mouth to the crater, Bomba slips inside via a secret underwater entrance. As soon as he dives into the water, however, Greg captures Lita and brings her to Pedro. Later that night, when Hardy finally allows his slaves to rest in the cave, Bomba attacks him, and although Kimbbo throws rocks at Greg to keep him at bay, Hardy overpowers and imprisons Bomba. In the morning, Bomba frees himself and the others, but just as he escapes, Greg and Hardy deliberately start a landslide which traps everyone else in the cave. While Pedro leads the slaves in an attempt to dig their way through the cave wall, Bomba watches Greg and Hardy race into the jungle. By swinging on vines and swimming through river short cuts, Bomba overcomes the two Americans just as they find a motor boat on the riverbank. He jumps on board and struggles with Hardy. At the same time, Andy and de Haven appear around the bend of the river, followed by Eli. Eli attacks de Haven, allowing Andy to shoot Greg. After Bomba knocks out Hardy, the three smugglers are rounded up on one boat, to be brought to the Commissioner. Pedro and Lita, safely out of the cave, join the party, but when Lita turns to thank Bomba, she finds that he has already slipped back to the jungle.