Moon rocket 4 launches from Earth the crew is pinned to their chairs by the enormous G forces created by the liftoff. On the radio frantic calls come from Earth asking them to report immediately. Finally the pressure eases and the commander of the flight Laird Grainger (Sonny Tufts) begins checking on the crew. Helen Salinger (Marie Windsor) the only female crew member and navigator is the first to respond as she shakes off the effects of the launch.
Grainger wants an immediate situation report from everyone. Helen confirms they are on course, which Grainger reports to White Sands control. He then hands off to the co pilot Kip Reissner (Victor Jory) Helen then offers a few words before allowing before letting Doug Smith (William Phipps) the ships radio operator speak. Finally Walt Walters (Douglas Fowley) the ships engineer sends a message home.
The ship is hit by something which Grainger believes to be a meteor thats now lodged itself in the rocket tubes. They decide to maneuver the ship wildly to dislodge the meteor. This succeeds but there appears to be damage to the ships engines. Kip volunteers to go and check the engines and donning protective equipment he enters the chamber. Kip finds a dangerous leak and begins repairs. Hes almost at the end of his strength when the situation is finally under control. In the control room warning lights blink out and the ship is saved.
Grainger queries Helen about her time on the radio, who she was talking to when she said Alpha we are on the way Helen is vague in her response and acts as if she recalls nothing. Grainger decides not to press the issue and asks her to begin preparing landing site locations. She has already chosen a site, a valley located on the dark side. Grainger is surprised by the choice it does not fit the mission profile but Helen is insistent, she admits she cant explain why, but knows it is the perfect spot.
The ship lands without incident and after discussing their options, the crew suits up and heads out onto the surface, Grainger goes first to inspect the ship and check if any repairs need to be done. He reports all is well and the rest of the crew begins to join him on the surface. Helen suggests they head towards a cave she saw of the crater they landed in.
As they begin to head to the cave a meteor passes low over them before impacting in the crater wall. Continuing they come to the Luna terminator. Grainger wants to highlight the danger and asks Helen for one of her lucky cigarettes she always carries. Throwing it into the direct sunlight the cigarette explodes in flames Drawing closer to the cave, Kip points out to Grainger there was no way Helen could have seen the cave during the landing as she claimed when suggesting to head towards it. Grainger dismisses the observation and orders the crew to continue into the cave.
Helen studies the walls of the cave for a few minutes then mentions it looks exactly as it did in a dream. From this point she takes the leads and begins threading her way through various passages. The crew discovers gravity is stronger in the cave, and the existence of stalactites hanging from the ceiling suggests moisture. For that to be true there must also be atmosphere. Realizing this they remove their suits to make exploration easier.
Helen continues to lead. Kip becoming increasingly suspicious insists on carrying his gun. Theyve only traveled a short distance when they are a attacked by a the size of a large dog. They beat the creatures attack off before Kip kills it with his gun. Disorientated during the melee, Helen stumbles off and encounters a second spider, also quickly dispatched by Kip.
Grainger and Kip decide to go back and retrieve the suits while Doug and Walt explore the chamber they are in now leaving Helen to rest. As she sleeps a strange female figure approaches and touches her palm leaving a strange mark. Helen wakes screaming as the figure rushes away
Grainger and Kip return and report the suits are missing. This forces the team to continue under the direction of Helen. The passage they are following opens to a huge cavern with a small walled city in the center. They enter and explore the city with all the evidence around them suggesting its been abandoned for a very long time. Kip is convinced Helen knows a lot more than she is admitting especially about the suits. Grainger intercedes and after an angry standoff Kip backs down.
Doug and Helen begin exploring another section of the city. Doug is in the lead and she stands back and allows a woman to attack him from a hidden position. The noise of the fight attracts the others but the unknown woman runs off before the party arrives.
As the men regroup they realize Helen is missing and spread out to search for her. More hidden women attack and try to take the men down individually. The crew fight of the attack and the mysterious women scatter except one who attacked Doug who he has pinned down. As the crew try to get a better look at her she disappears into thin air, leaving everyone stunned as to what has just happened.
Helen finds her way into a secret passage and encounters the leader of the women, Alpha (Carol Brewster) she is then introduced to Beta (Suzanne Alexander) and Lambda (Susan Morrow) Helen is confused and unsure of herself till Alpha tells Helen she is now one of them. Alpha goes on to describe how she has been sending mental messages across space and coaching Helen with all the knowledge she needed to become the navigator selected for the mission.
Alpha then tells her the history of their existence on the Moon. A decision was made eons ago to reduce the population as air and other resources began to run out. What Helen sees now is the final generation trapped in the caverns. Their only hope was a spaceship arriving from Earth. Alpha plans to learn how to fly the ship then disposed of the crew with the exception of Helen will take three of the Moon women back to Earth.
The Moon women accompany Helen back to the main party, Helen then introduces the women to the crew and food and drinks are served. Kip refuses to be engaged in any of the entertainment or food, deciding to remain isolated and eat his own rations.
During the dinner Doug asks Lambda why there are no men. She explains they all died off when she was a child and Doug is the first man she has ever seen. At another table Grainger is questioned by Alpha as to the workings of the ship, he explains he cant tell them anything. Because he is under orders not to reveal such information
Walt is charmed by Beta who fills his head of stories about caverns filled with gold. In fact there is so much no one bothers to mine it. She promises to let Walt have the gold if he agrees to take her back to Earth with him. Doug falls heavily for Lambda, he does not realize she can read his mind and is drawing information to build rapport to look as though she genuinely likes him.
Alpha calls the women together and they leave for the night, the crew begins to discuss whats happening when they realize Walts missing. Helen mentions he went somewhere with Beta. Grainger starts to argue with Kip who is convinced the situation is not as it seems.
Kip again challenges Helen, at first she resists then goes through a mental convulsion which seems to release her true self. She warns Kip of the Moon Womens plan and their intention to harm the rest of the crew and only take her back to Earth. As the moment of clarity strengthens she admits she likes Kip more than Laird however the Moon Women are forcing her to show interest in Laird because he knows more about the ship.
Kip finds Laird and apologies for his earlier behavior without revealing any of the conversation hes had with Helen. Meanwhile Walt has taken Beta back to the ship and is explaining the various functions. She in turn reaffirms her promise about the gold.
During the night the women begin a dance. Doug, woken by the music wakes and goes to watch. Kip spots Doug and sees his growing interest in Lambda, after a few minutes they go off together. Kip reports back to Helen who warns him Lambda is one of the most dangerous ones
In the caves Walt is shown the gold, he is overjoyed and begins to celebrate until Beta kills him with a knife. Elsewhere Lambda breaks down and tells Doug she actually loves him and is no longer acting. She then explains the plan to steal the ship. She makes him promise that if they escape she wants him to return and rescue the remaining women
Lambda then approaches Alpha with a recommendation one of the men be allowed to return with them as a sign of good faith. Alpha rejects the suggestion, angry at the thought of losing Doug Lambda threatens to unravel the entire plan Alpha and Beta ignore Lambdas ultimatum but do decide to accelerate their plans and go off to execute the men. Doug finds Kip and tells him Lambdas story. Kip confronts Laird and Helen and argues Helen is leading the attack. Kip grabs Helens hand and covers the device in her palm being used by the Moon Women to control her.
She admits her role in the plot and she actually loves Kip and not Laird. This causes the men to get into a fight. Lambda arrives and sounds the alarm; the women are stealing the ship. Unknown to Alpha and Beta, Lambda has hidden two suits for the men.
Lambda tries to stop the two women, but is killed by Alpha. In turn Kip and Laird catch up with Alpha and Beta who have Helen with them. A gun fight ensures and the two Moon women are killed but Helen avoids injury
The crew then it back to the ship, report the situation to Earth and liftoff for home