Following the Proffesor's latest (unsuccessful) attempts to make tea, he goes to the trading post to try to persuade Dumont to trade something for a box of Earl Grey. Dumont obliges, when Jane persuades him that 'a good deed can be its own reward', which Tarzan overhears her saying. As they are about to leave, none other than those less-than-friendly-diamond-miners, Neils and Merkus arrive. They want to search for their lost diamonds, and Tarzan reluctantly allows them on the condition that they leave the gorilla family alone. While mining, Neils and Merkus are attacked by Tublat, the banished bull-ape enemy of Tarzan and family. However by some lucky turn of fate, the dynamite goes off close to the creature and injures him, and the devious miners decide to cage him and sell him. Tarzan arrives, and tells Neils and Merkus that he doesn't mind if they take Tublat, or even kill him. When the gorillas find out that Tublat is gone, they celebrate, but Tarzan feels guilty and leaves them to be by himself. Jane talks to him, and he explains that even though Tublat is his enemy he is going to set him free, because the jungle is his home too and its not fair to take him out of that. Jane is unhappy with his decision, but then he repeats back to her what he heard her say, that 'a good deed can be its own reward', and she lets him go.