Tarzan is joined by a reporter and her fiance on a journey to find a boy who was abandoned in the jungle six years earlier. The search party must also battle an evil native, who is out to kill the boy and take over as chief of his brother's tribe.

On the eve of his wedding, John Clayton, Lord of Greystoke (better known as Tarzan), receives a message from the witch doctor Mugambe that his homeland is in danger. It turns out that a treasure hunter named Ravens is searching for the lost city of Opar, and is destroying the jungle and desecrating the villagers' burial grounds in the process. Only Tarzan can stop Ravens and set things right in the African jungle, but will Jane stand for her fiance being away for so long?

The plot follows the novel more closely than does any other Tarzan movie. John and Alice Clayton take ship for Africa. Mutineers maroon them. After his parents die the newborn Tarzan is taken by a great Ape, Kala. Later the boy finds his father's knife and uses it to become King of Apes. Binns, the sailor who saved the Claytons and who has been held by Arab slavers for ten years, finds the young Tarzan and then heads for England to notify his kin. A scientist arrives to check out Binns' story. Tarzan, now a man, kills the native who killed Kala; when their chief is killed the black villagers appease Tarzan with gifts and prayers. The scientist's daughter Jane is carried off by a native, rescued by Tarzan (who has burnt the native village), aggressively loved by him ("Tarzan is a man, and men do not force the love of women"), and at last accepts him with open arms.

A letter from Jane, who is nursing British troops, asks Tarzan's help in obtaining a malaria serum extractable from jungle plants...

An expedition seeking to bring Jane back to civilization, and Tarzan into captivity, gets more than it's bargained for.

The idyllic life of Tarzan and Jane is challenged by men on safari who come seeking ivory, and come seeking Jane as well.