A letter from Jane, who is nursing British troops, asks Tarzan's help in obtaining a malaria serum extractable from jungle plants. Tarzan and Boy set out across the desert looking for the plants and wind up ruining a German's attempt to capture a wild horse. They arrive in an Arab city and rescue a stranded American lady magician, sentenced to be hanged for carrying a secret message to the Sheik. To obtain the plants, Tarzan must fight prehistoric monsters, Nazis, and so on.