A scientific expedition to the Moon encounters a race of cat-women, the last survivors of a two-million-year-old lunar civilization. Residing deep within a Moon cavern, where they have managed to maintain not only the remnants of a breathable atmosphere and Earth-like gravity, but also a pair of gigantic Moonspiders, the cat-women wear black unitards, have beehive hairstyles, and wear elaborate cosmetics. Realizing that their remaining atmosphere will soon be exhausted, the cat-women plan to steal the expedition's spaceship, migrate to Earth, and in the words of the cat-women's queen, Alpha, "We will get their women under our power, and soon we will rule the whole world"!
Through the use of their telepathic abilities, the cat-women have been subliminally controlling Helen Salinger, the mission navigator and only female member of the Earth expedition. Once on the Moon, the cat-women take control of Helen's mind, after which she leads the entire crew to the cat-women's cavern. Although unable to directly control male minds, the cat-women are able to influence the male crew through Helen, using their own superior intellectual abilities and feminine wiles. As explained to Helen by the cat-woman Beta, "Show us their weak points. We'll take care of the rest".
Along with telepathy, the cat-women can transport themselves, unseen and instantly, from place-to-place within the cavern. They use this ability to steal the crew's unguarded spacesuits. This forces the crew deeper into the cavern and into violent confrontations with the two moon-spiders and the cat-women. Failing to exterminate the men, the cat-women approach them openly, using Helen. Kip, who has always been suspicious of the cat-women, confronts Alpha about the missing spacesuits. She promises to return them in the morning. Food and drink are then brought, and private conversations between both groups begin. As these progress, the gun-wielding Kip sits alone, unable to intervene, while the cat-women successfully manipulate expedition commander Laird and the other men.
By that evening, the cat-women have learned how to pilot the spaceship. Walt is stabbed to death by Beta. Lambda has fallen in love with crew member Doug and tells him of the cat-woman plot, saying, "I love you Doug, and I must kill you". The male crew now realizes that they are in danger. Carrying three spacesuits, Alpha, Beta, and Helen make a break for the spaceship. Lambda teleports ahead to delay them and is bludgeoned to death by Beta. Kip catches up, and fires several shots, killing Alpha and Beta, but leaving Helen uninjured. The surviving expedition members escape the cavern, reach their spaceship, and return to Earth.
Upon the film's release, Variety magazine wrote: "This imaginatively conceived and produced science-fiction yarn takes the earth-to-moon premise and embellishes it with a civilization of cat-women on the moon... Cast ably portray their respective roles... Arthur Hilton makes his direction count in catching the spirit of the theme, and art direction is far above average for a film of this calibre. William Whitley's 3-D photography provides the proper eerie quality". The New York Times wrote: "They try to get their hands on the visitors' rocket ship, hoping to come down here and hypnotize us all. Considering the delegation that went up, it's hard to imagine why". The Encyclopedia of Science Fiction calls the film absurd, but notes that it "qualifies as one of the most influential science-fiction films ever made" as it influenced later films "in which astronauts discover decadent, all-female civilizations on other planets, including Fire Maidens from Outer Space, Queen of Outer Space, Nude on the Moon, Voyage to the Planet of Prehistoric Women."
