Shaka, a friend of Tarzan, brings Jane a deadly variety of spider that has already killed five people in his village, in hopes that she can find an antidote to the poison. Cheetah accidentally drops the jar containing the spider on the floor, breaking it an letting the spider escape. When Shaka pushes Jane away, the spider bites him. Although there is no known antidote, Tarzan remembers that a plant which grows many miles away in the Urongo Basin and is eaten by a local tribe to make them immune to spider bites. Tarzan, Jane and Shaka rush off to find this plant before it's too late. Shaka warns them, however, that the poison makes the victim delirious and extremely violent and that he could be a danger to them on the trip. Tarzan leaves Jane and Shaka an swings off on a vine to continue his search for the antidote. The poison takes a stronger hold on Shaka and he begins to get violent. He drags Jane to a tree and ties her to it yelling that she is evil and must pay. He begins to hallucinate that Jane is his lost love, Michelle, who deserted him in London for another man. Nothing Jane says will make him believe that she is not Michelle. He is determined that Tarzan is the other man and makes plans to kill him. Tarzan reaches the Urongo Basin and gathers the plants he needs to help Shaka. When he returns to where he left them, Shaka attacks him with a knife. Shaka, in his demented state is stronger than a normal man and gives Tarzan a good fight. Eventually, however, Tarzan subdues him and Shaka collapses on the ground. Tarzan grinds up the leaves of the plant, mixes them with water and forces the liquid into Shaka's mouth. He regains consciousness and begins to return to his normal self. When they return to camp, Dan tells them that the doctors at Bandali are very close to developing a serum for the spider bites thanks to Tarzan's information about the plants. Tarzan gives Shaka the rest of the antidote he made and he returns to his village to help his people.