Five astronauts travel to the dark side of the moon on a scientific expedition. There they discover a cave which somehow retains a breathable atmosphere. They remove their space suits and venture on, soon finding a buried city where the last members of a 2 million year old civilization greet them with food and drink. Little do they know that these eight lovely leotard-clad women are planning to steal their ship.

On their voyage into outer space, the crew of Moon Rocket 4, the first American astronauts to go to the moon, awaken from their long sleep and make contact with Earth. When the crew, comprised of Commander Laird Grainger, co-pilot Kip Reisner, navigator Helen Salinger, engineer Walter Wallace and radio operator Doug Smith, make brief statements for the listeners on Earth, Laird is puzzled by Helen's cryptic message that states "Alpha, we're on our way." After the ship is struck by a meteorite, Laird maneuvers the vessel to shake the rock loose by centrifugal force. Kip then goes into the atomic chamber to douse the resulting fire. Without consulting her navigational charts, Helen advises Laird to land the ship in a valley on the dark side of the moon. The astronauts don space suits following the smooth landing and leave the ship to explore the moon. Helen points the way to a cave on the edge of a crater where, deep inside a cavern, they determine that the cavity has an oxygen atmosphere. After removing their helmets and space suits and leaving them behind, the crew continues farther into the cave. Two giant spiders attack Helen, but she is saved when Kip kills them with his gun. Now concerned for their safety, Kip and Walt go back to guard the space suits while Laird and Doug walk ahead, leaving Helen to recover from the attack. While she is resting, someone caresses her hand and disappears. Helen is startled awake and discovers a small white disk in her palm, but hides it from her comrades and insists they continue. Walt and Kip return and inform them that their space suits have disappeared. After walking farther into the caverns the crew is surprised to discover a small city nestled in a vast valley. Kip's suspicions of Helen intensify when she seems to have prior knowledge about the place. When Helen and Doug leave the group to explore alone, she hangs back when he is attacked by three unidentified women. However, the women disappear when the the rest of the crew show up and discover that Helen has also vanished. While the men decide to wait an hour for her to return, Helen meets the residents of the moon, "cat-women" whose leader is named Alpha. Alpha explains that because of the moon's deteriorating atmosphere, their ancestors were forced to conduct planned genocide and oxygen preservation so that a few of their species would survive. Their only hope of continued survival is to leave the moon. Using telepathy, Alpha drew Helen to their location, and now plans to get rid of the men, whom they cannot control, and fly back in the rocketship to dominate the earth. Helen returns to introduce the cat-women to her companions. Alpha assures them that she will return their space suits the next day. Kip remains suspicious, however, and refuses to eat the food served by the cat-women. While the rest of the crew is eating, Walt secretly goes with cat-woman Beta to see a cave filled with gold. After the cat-women retire, Kip draws Helen into another room and admits that he would fall in love with her if she were not already involved with Laird. When Kip embraces her, Helen is released from the cat-women's control and she confesses that the cat-women, who plan to kill all the men, also compelled her to seduce Laird because he is the ship's commander. Once Kip releases Helen, she once again falls under the spell of the cat-women, but neither reveals their conversation to Laird. Meanwhile, Beta takes Walt to the rocketship so he can show her how to operate the ship. She then takes him to the cave and while he is distracted by gold embedded in the walls, she murders him. Late that night, Doug is lured away by Lambda, another cat-woman, and they confess their love for each other. Lambda then warns him that he is in danger. At the same time, Kip awakens and after a fruitless search for Doug, returns to find Helen in Laird's arms. After Kip encircles her in another tight embrace, Helen is freed from the mind-control and admits she loves only him. Laird strikes Kip but they discontinue fighting when they realize that Helen has run away. Shortly afterward, Lambda and Doug arrive to warn that the other cat-women have mobilized and plan to steal the rocketship. Lambda attempts to stop the cat-women but is murdered by Beta. After Kip and Doug find her body, Kip runs ahead and kills the rest of the cat-women. The astronauts return safely to the rocketship and, with their navigator back to normal, they signal Earth of their intention to return home.