When Tarzan receives a letter from Jane, who is serving as a nurse in a London hospital, asking him to send fever medicine for her ailing soldier patients, he allows Boy and Cheetah to accompany him across the desert and to the jungle in which the fever medicine plant grows. At the edge of the desert, Tarzan sees a group of men led by Karl Straeder trying to capture Jayne, a wild stallion. Tarzan orders the men to free the stallion, and in gratitude, Jayne allows Boy to ride him to the oasis. At the oasis, meanwhile, American magician Connie Bryce confers with Sheik Amir. Amir, the leader of a desert tribe, asks Connie to deliver a message to his old college friend, Prince Selim, the son of Sheik Abdul El Khim, who rules from the city of Bir Herari. Amir's previous messengers have all met with death, and so he cautions Connie as he hands her the message, which he has hidden in a bracelet. After Amir departs, Connie meets some nomads who ask her to demonstrate her magic skills. Connie obliges by asking them to saw her in half, and when Tarzan approaches the oasis, he sees the nomads sawing Connie, and believing that she is in danger, chases them away along with Connie's horse. Upon discovering his mistake, Tarzan offers to escort Connie to Bir Herari. As Tarzan rides into town with Jayne, Karl and his accomplice, Paul Hendrix, accuse him of stealing the horse. Arrested and jailed, Tarzan entrusts Boy to Connie's care. When Hendrix then presents the stallion as a gift to the sheik, Prince Selim questions his motives and warns his father not to trust Hendrix. Later in the town square, Cheetah diverts the populace by performing a high-wire act while Connie arranges to meet the prince later that night. That evening, an emissary from the prince escorts Connie to the palace, where she delivers the bracelet to Selim. As Selim reads the message from Amir, warning that Hendrix is a foreign agent who is arming the tribesemen, Hendrix and Straeder watch from the window. After Connie leaves, they sneak into the palace and kill the prince, but before they can steal the bracelet, Cheetah snatches it and flees. When Hendrix accuses Connie of murdering the prince, she is arrested and sentenced to be hanged. Desperate, Boy and Cheetah help Tarzan escape from his cell, and as Connie is escorted to her execution, Tarzan mounts Jayne, gallops to the town square and sweeps her from the gallows. Fleeing into the desert, Tarzan, Boy, Cheetah and Connie are pursued by Hendrix and his men. Engulfed in a sandstorm, they take refuge in a camel driver's hut. After the storm subsides, Tarzan and his party head for the medicine jungle, and are trailed by Hendrix and his henchmen. Upon reaching the jungle, Tarzan leaves Boy, Cheetah and Connie and goes to search for the medicine plants. Spying Hendrix and Straeder on their trail, Boy, Cheetah and Connie retreat into the jungle and are followed by the agents. After Straeder is mauled by a lion, a prehistoric lizard climbs out of the underbrush, sending Connie and Boy running into a cave for shelter. There Boy gets caught in a giant spider's web, and Cheetah scurries to alert Tarzan of his peril. As the massive spider crawls toward his cave, Tarzan swings across the jungle to the rescue. Hendrix, who has trailed Connie to the cave, trains his gun on her just as Tarzan swings down from a tree and shoves him into the spider's web, where the spider devours him. After Tarzan frees Boy from the web, they all return to Bir Herari. There, Connie delivers Amir's message to the sheik, thus averting war. Tarzan then entrusts her with the fever medicine to take to Jane in London and their mission completed, Tarzan, Boy and Cheetah return to their home in the jungle.