The jungle king fights to protect a lost city of gold from an international criminal.

In Central America, a little native boy, Ramel, is abducted by Vinaro, a madman who believes the child to be the sole link to a lost Aztec city of gold. Vinaro uses one of his diabolical explosive mechanisms to eliminate police and army officials; and the legendary Tarzan is flown in to help locate the jungle city. After trading his civilian clothes for a leather loincloth and a knife, Tarzan sets out on his mission, aided by a chimpanzee, a jaguar, and a lion. He rescues the boy, saves the life of Sophia Renault, Vinaro's former mistress, and finds the secret caves that lead to the lost city. Once there, however, Tarzan is unable to persuade the aged chieftain, Manco, that he must resort to violence if he is to protect his city from Vinar. Consequently, when the madman arrives with troops and armored tanks, Manco offers him a fortune in gold. The insatiable Vinaro demands more, and Manco leads him into a chamber where Vinaro pulls a lever and releases a shower of gold dust that entraps and suffocates him. Simultaneously, Tarzan engages the mercenaries in battle and successfully defeats them. As Manco observes sadly that violence is sometimes necessary to preserve one's way of life, Tarzan and Sophia leave the valley of gold and return to modern civilization.