At a hospital in the African jungle located between the city of Randini and the native village of Nigasso, white physician Dr. Sturdy struggles to find a cure for a lethal fever. Since the recent death of the Nigasso chief from the fever, Futa the medicine man has convinced the tribe to cease helping Sturdy with his experiments. Sturdy’s daughter Anne, who is uneasy about the tensions, goes into the jungle to welcome her fiancé, Ken Warwicke, who is returning after spending two years in England completing his medical degree. Pleased to be back in Africa, Ken is initially dismissive of Anne’s concerns, until they are attacked by several Nigassos, led by Ramo, Futa’s advisor. Anne, Ken and his carriers are rescued by Tarzan, a white man brought up in the jungle, who is friendly with all the surrounding tribes. While Tarzan escorts Anne and Ken safely on to the hospital, Ramo returns to Nigasso with some of the medicine stolen from Ken’s supplies. Futa insists that his own medicine is stronger, however, and destroys the supplies. After welcoming Ken at the hospital, Sturdy explains that the growing tensions between him and the Nigasso have been intensified by a cautious ruling council who will govern the village until the boy chief comes of age. When Sturdy states that Futa has forbidden the natives to donate blood to the hospital, and therefore the blood bank is nearly depleted, Tarzan vows to mediate. At Nigasso, Tarzan meets with Futa and accuses him of being jealous of the white doctors, but Futa declares that the doctors are evil. When a native woman, Tochina, then falls into the river, Tarzan rescues her, but not before she is severely bitten by a crocodile. Futa condemns Tarzan when he insists on taking Tochina to Sturdy for treatment. At the hospital, Sturdy amputates Tochina’s mangled leg, but worries about having no blood to give her a transfusion. Before Tarzan returns to his home to his wife Jane and son Tahtu, Sturdy gives him medicine and a thermometer for Jane, who has been experiencing pains that the doctor believes may be appendicitis. That evening, Jane experiences pain and when the thermometer registers a fever, Tarzan decides to take her down the river to Sturdy. In the Nigasso village, Futa refuses the request of Tochina’s sister to go to the hospital to donate blood for her sister. As a result of not receiving a transfusion, Tochina dies. In despair, Tochina’s husband Molo returns to the village for guidance. When Ramo sees Tarzan arrive at the hospital with Jane and Tahtu, he reports to Futa that Jane is ill. The medicine man then hypnotizes Molo, ordering him to kill Jane in retribution for Tochina’s death. Futa gives Molo a charm necklace and sends him to the hospital, where Sturdy has successfully removed Jane’s appendix. Later, Nigasso sentries stop Amuka, a messenger from the former chief’s mother, known as the Old Mother. Amuka confides to the guards that the boy chief has contracted the dreaded fever and since the Old Mother and the boy’s mother have no faith in Futa, they wish the services of Sturdy. The guards allow Amuka to pass, but he is later captured by Futa’s men. That evening Tahtu and his pet chimpanzee Cheta overhear Futa torturing Amuka to learn his mission. When Tahtu leaves to inform Tarzan of the situation, he is chased by one of Futa’s warriors, but evades him. After Amuka finally reveals the young chief’s illness, Futa wavers, fearful that should the boy die, the villagers will stone him. Ramo then suggests that they steal Sturdy’s serum to cure the boy chief and Futa uneasily agrees. After Tahtu tells Tarzan of Amuka’s torture, Tarzan orders him to remain with Jane and goes to Nigasso where he finds Amuka unconscious. Futa and Ramo secretly slip into the hospital where Ramo knocks out Sturdy’s native aide and breaks into the medicine cabinet. Unknowingly, Ramo steals a bottle of poison and escapes just before Tarzan returns with Amuka. As the revived Amuka reveals the young chief is ill, Sturdy discovers the broken medicine cabinet. Anne then finds the groggy aide and discovers Ramo’s break-in. Realizing that Ramo has stolen the poison, Tarzan hastily departs for the royal Nigasso cave lair. After Tarzan’s departure, Tahtu discovers Molo in Jane’s room and, spotting the strange necklace, goes to ask Sturdy’s native aide its significance. Alarmed by Tahtu’s description of the necklace, the aide rushes to Jane’s room and finds Molo strangling her. In the ensuing struggle, the aide kills Molo. Tarzan takes a dangerous shortcut to the royal hideout and is captured just outside of the caves as Futa prepares a sunset ceremony to save the young chief. The head of the council approves Futa’s requests, including his demand for the heart of a young lion. When Tarzan is brought to the cave bound, Ramo suggests that Futa use Tarzan’s heart instead. As sunset approaches, Old Mother and the young chief’s mother plead with the council to allow them to take the young chief to Sturdy, but are refused permission. Meanwhile, Tarzan breaks his bounds and attacks Ramo and the warriors who have come to kill him. As the sun sets, Futa begins the ritual to heal the young chief, but Tarzan interrupts the ceremony and explains the serum is poison. When Futa refuses to believe him, Old Mother suggests Futa test the serum on himself and the council concurs. Despite Tarzan’s attempt to stop him, Futa drinks the poison and moments later dies. When Old Mother renews her pleas to take the young chief to Sturdy, the council finally agrees. Back at the hospital, Sturdy, Ken, Anne, the now recovered Jane and Tahtu hear the news from the native drums and are soon joined by Tarzan.