The Professor learns about a spiritual silver ape that, supposedly, cures the injured of the jungle. Not believing this is a spiritual creature, he plans to study it more. But when Philander steals his notes and finds out about the ape, he plans to capture it.

Count Nikolas Rokoff hears about a treasure in the valley of the leopards and plans to find it. Tarzan doesn't want to help, until Rokoff threatens to hurt Jane if he doesn't.

Two sneaky men named Johannes Niels and Merkus come and want Tarzan to take them to the volcano on the other side of the jungle to look for diamonds. Tarzan agrees as long as he gets a diamond for Jane in return. Little does he realize that the men are not planning to keep up their side of the bargain when the diamonds are collected—or that his friends are following them.