An expedition to the Moon encounters a race of "Cat-Women", the last eight survivors of a 2-million-year-old civilization, deep within a cave where they have managed to maintain the remnants of a breathable atmosphere that once covered the Moon. The remaining air will soon be gone, and they must leave if they are to survive. They plan to steal the expedition's spaceship and migrate to Earth. Through the use of their telepathic ability, the Cat-Women have been subliminally controlling Helen Salinger (Marie Windsor) so she can win the navigator slot on the expedition and lead the crew to their location. Once Helen and the male members of the crew arrive on the Moon, the Cat-Women take complete control of her mind. They are unable to control the men's minds, but they work around this obstacle, with Helen's help, and the use of their superior abilities and feminine wiles. "Show us their weak points", one says to Helen. "We'll take care of the rest". Along with telepathy, the Cat-Women have the ability to transport themselves unseen from place to place in their living space. They use this ability to steal the crew's spacesuits from the mouth of their cave, where they were left unguarded.
