 After landing on the 13th moon of Jupiter, the men from Earth debark from their ship to find a forested area containing the last remnant of lost Atlantis: an old man named Prossus, a bevy of nubile young women eager for husbands, and -- The Creature. "The beast with the head of a man," laments Prossus. "It must be destroyed -- yet it is indestructible!"