Alone in the jungle, Tarzan gets chased by Sabor the leopardess to a rocky place known as the Dark Mountain. When the echo of the monster calls, Sabor runs away just as Tarzan is encountered by two hulking, spoiled gorilla brothers, Uto and Kago, and their controlling, over-protective mother Mama Gunda. They fear the Zugor as much as Tarzan does, and when the booming call of the monster again echoes through the valley, the trio flee and Tarzan is able to escape Dark Mountain. He encounters a crotchety old gorilla who at first keeps the boy distant, but Tarzan discovers this gorilla is actually named Zugor and was pretending to be the monster. He uses hollow trees as megaphones to amplify his voice and pretend to be a monster, scaring other jungle creatures away from his territory and food. Tarzan uses this discovery to blackmail Zugor into letting the boy stay with him. Thanks to Tarzan's cheerfulness and helpfulness, Zugor begins to warm up to him. Tarzan continues to try to figure out what he is along with Zugor, but they both promise not to tell anyone.