Tarzan and Dr. MacWhirtle visit a land inside an extinct volcano. There they assist Ruandi, a young tribesman, in rescuing his beloved, Lula, from the machinations of the witch doctor Kuvuru.; While Tarzan is away from home, visiting Pal-ul-don, Sheikh Ibrahim kidnaps Jane and Boy. Tarzan rides to their rescue on a gryf.; While exploring, Boy and Dombie are captured by the men of a small village. They witness the sacrifice of a man to a horned monster. While they are attempting escape, Boy realizes that the monster is the witch doctor in a costume. He and Dombie steal the costume and use it to terrorize the village.; The patriot army attacks Amotu and Mothibi manages to capture Nagopa.