A team of astronauts lands on a moon of Jupiter to find it populated with beautiful young women looking for mates. An old man explains to the explorers the group's story, as well as the moon's dangers.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!"