Jane's friends, Eleanor, Greenly, and Hazel, thinking Jane is in trouble, come to rescue her. When they find her and everything is explained, they fret Jane has changed. To prove she hasn't, Jane takes them on a picnic in the jungle. That's when trouble comes up.

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.