We see an atomic explosion as the opening credits begin.
A group of military servicemen huddle around a radio trying to reestablish contact with rocket ship XRM. At the Pentagon, concern grows over the lack of contact. The last message from the ship was cut off mid in mid sentence, which many point to as a sign a disaster has occurred. A newscaster describes how man's first flight into space seems to have ended in disaster and grave fears are held for Doctor Eldon Galbraithe and his crew. The last message was received as the ship entered Mars orbit and nothing has been heard since.
We cut to a scene of a rocket approaching Mars. The radio operator Herb Ellis (Rod Taylor
) reports to Dr. Galbraithe (Nelson Leigh
) that contact with Earth is lost. He is sure it is not the equipment because the signal was lost as the ship entered Mars' magnetic field. Galbraithe asks John Borden (Hugh Marlowe
) to check the viewer. Across the landscape are strange green surface markings, but from orbit they can't make out what the markings are.
Dr. Galbraithe gives Henry Jaffe (Christopher Dark
) orders to lay in a course back to Earth. Their mission was only a recon mission; simply do a couple of orbits of the planet then head back for Earth with their findings. As the ship breaks Mars orbit, it runs into a strange time dilation effect that accelerates the ship unbelievably. Before the crew can try to slow the ship down they are pinned to the deck by the incredible G force.
They wake to find they have landed high up on snow covered mountains. They think they are on Mars, specifically one of the poles. However Bordon realizes that something is not right. The gravity feels too strong and he suspects there is an atmosphere outside. They take a chance the crack the hatch to see what's going on.
Checking the ship they find the control surfaces have been damaged, also the radiation count is about three times higher than would be expected on Earth. Herb tries the radio and is unable to make any contact or find any evidence any radio broadcasts even exist.
The team decides to hike down below the snowline and investigate the rest of the area. Herb quips that if they're on Venus, they may run into some high domed types that might kill them with ray guns. To try and stop that we only have good old revolvers.
During a rest period one of the crew finds a cave and decides to explore it. As they go deeper they discover spider webs. As they ponder what may have spun it, Herb is attacked by a giant spider. As they fight the creature off with gun fire, a second spider attacks.
After marching most of the day they decide to make camp. While sleeping, they are ambushed by a band of caveman type creatures. The party survives the initial attack and drives the attackers off. One of the creatures was killed and when the corpse is inspected it appears to be a Cyclops.
At first light the party moves off again working their way further down the mountain. They encounter the ruins of what appears to be a graveyard, and looking at the tombs they realize they are on Earth, and from the dates, they can see some period in the future.
Galbraithe explains there is a theory that if you can move fast enough you can affect time, and actually move backwards through it. Bordon wonders if the instruments failed at 100 miles per second, but they may have been travelling many times faster. They also are unable to decide how long they were actually blacked out.
They work their way around the cemetery trying to discover the oldest gravestone. They do find a number marked 2188, and even these look old. Galbraithe considers whatever happened, he presumes a nuclear war given the high background radiation, and it would take at least a couple of hundred years for things to become livable again.
They work their way along a valley and see a mountain range in the distance. It is decided they must be the Rockies (In Western USA) and judging from the environment and weather they may be either in Colorado or New Mexico.
In the distance they see a thin column of smoke; Borden decides it is not a brush fire and might have been set by somebody. He decides to go and investigate but is attacked by another group of the mutated humans. The rest of the party rescues Borden and withdraws as they realize the mutants are getting behind them. They take shelter in a cave to regroup and decide their next course of action.
Borden recovers from the attack being little more than a little shaken up. The party can't decide if they are trapped or found a place of safety. While exploring the cave they find a stainless steel barrier blocking access to the rest of the tunnel. Suddenly a second barrier slides into place and the first barrier opens. Short of any real options they decide to explore what's behind the barrier.
They follow a long tunnel of advance design until they encounter a room. A disembodied voice speaks to them and instructs them to leave all their weapons and packs behind and enter into another tunnel. There they are greeted by a human dressed in futuristic clothes. The room is set up like some form of court or council meeting area.
Timmek (Everett Glass
) introduces himself and explains it was his voice the party heard. Timmek queries why they are here. Borden explains they took refuge in the tunnel, and that they had flown to Mars in 1957. Timmek explains they encountered a time dilation effect. And since they had been away, civilization had encountered the great blow. Timmek explains it was an Armageddon atomic war. Timmek is unaware of any other surviving elements of civilization.
Other members of Timmek's group begin querying the men on their intentions, especially why they feel the need to have weapons. Borden has no specific response to this and the council decides to keep the guns from the men.
Garnet (Nancy Gates
) Timmek's daughter appears and reminds her father the men must be both tired and hungry. Galbraithe asks about what year it must be, Timmek tells him it is 2508AD. Stunned the men follow Garnet and are fed a wide variety of food.
Garnet explains that all their food is produced underground due to the high radiation counts. She then introduces Elaine (Shirley Patterson
) she is Elda's Stanley Fraser
) assistant and makes an offer to show the crew anything they would want to see. Galbraithe wonders why the people have not conquered the surface. Garnet explains the people are tired of war and have generations of tradition behind them.
As the conversation peters out Galbraithe notices one of the servant girls Deena (Lisa Montell
) and asks about her. Garnet explains she is from the surface; shes been saved when she was rejected by the beasts (deformed humans) on the surface.
The four men decide to bunk down for the night, Jaffe asks Borden if these people may have learned how to reverse the time dilation effect they suffered. Borden thinks probably not. He thinks that those who survived the war, turned their technology inwards, only applying what they needed to survive. Borden thinks these people will be ultimately useless to their needs.They are gutless and not willing to get out of their holes
Next morning Elaine arrives to take Galbraithe to meet the chief science councilmen. At the meeting he explains he wants to repair the ship so he can explore the rest of Earth, find out if there other surviving colonies. The council rejects the idea. They have no weapons or desire to fight the beasts to retrieve the ship
Later Garnet comes across Borden alone in his quarters; he asks if she would mind showing him the sites. She reacts be saying she'd hoped he would ask. In another part of the colony a science worker explains to Jaffe where their power and food come from. The science worker slips and mentions the colony is getting smaller and the drain on resources is becoming less and less
Borden and Garnet discuss the sadness surrounding Jaffe, how he left a family behind, and what sort of courage did it take to fly in the first place. Mories (Booth Colman
) interrupts the conversation and Borden sense a bit of jealousy from the man. Garnet explains he will probably succeed her father as leader of the council, and as such took it for granted Garnet would be his partner.
Back at their quarters Herbert tries to apologize to Deena for a previous comment but she refuses to hear him. Borden and Galbraithe return from their respective meetings and agree the people underground have lost their will, their desire to push frontiers. He then admits he has a date with Garnet, and when the others tease him about it he explains Garnet is going to show him a tunnel that leads back to the surface.
Garnet takes Borden to the tunnel and they go outside. Garnet is surprised at the beauty of the Moon; it is not how the books describe it. Borden grabs garnet and kisses her. She declares he love for him. Hes concerned by this emotion and says that at some stage he will have to leave. Garnet begs him to stay and make his life with the colony.
Again at their quarters the men try to communicate with Deena. Borden explains they are trying to help her people. Finally she breaks down and accepts Herberts apology. Jaffe and Galbraithe return from another meeting with the council. Jaffe explains the colony seems to be in real trouble. He visited a hospital and found only 14 children out of a population of 2000. Jaffe doesnt think they have more than more generation.
Unknown to the men, they are being spied on by Mories, who becomes unsettled over Bordens plans for Garnet. Mories goes to the council twists the story of their intention. Mories convinces the council to ignore their requests
Back at the quarters Deena tells the rest of her story. Most of the normal children were not driven away by the beasts but actually put to work by them. At the end of the conversation Herb comes in and Deena admits her interest in him
At the council meeting Galbraithe pleads his case to allow them men to expand to the surface and have invited those in the colony who want to be part of the expansion. Mories pleads the counter case that the men are going to enslave everyone in the colony and carries the day and the council votes down the proposal.
That night Mories steals the mens weapons accidentally killing one of the councilmen in the process. He then hides the gun in the men's quarters and rushes of to tell the council the men stole their weapons. Deena sees him, and tries to retrieve the guns.
Deena sees Herb kissing another woman and becomes jealous and distressed. Mories reaches the council and realizes the dead councilman has already been found. The council go to their quarters and discover the guns and
Timmek orders the arrest of the men.
Deena stands back and says nothing of what she saw. At the council chamber the men a presumed guilty, they are going to be banished from the city, taking only what they came with.
Deena realizes what this means and goes to Timmek. As she waits to see him Mories attacks and tries to kill her, unsuccessful he escapes into the tunnels as she reveals what had occurred. They follow him to the outside world in time to see him killed by the beasts.
Sometime later the council apologizes for their actions. 20 or so men have volunteered to go out to with the crew. They need to resolve the issue of weapons. Deena tells them only the ugly beasts fight and there is not as many of them as people thing
The crew decides a primitive form of bazooka will be the best way to kill those on the surface. Deena tells them that the beasts follow a leader, who is selected for his ability to fight off any rivals. She believes if they kill him, the rest could fall into line pretty fast.
The four men go outside to test the weapons. They fire at a pass that looks set up like an ambush, they fire around into the area and the beasts run away in confusion. One of them not mutated like the others is captured and taken back to be questioned.
The captured enemy tells Deena that the leader of the beasts will probably take his people back to the caves to make it harder for the humans to attack them. On the way they find another normal surface dweller speared by his own people.
They find the possible hiding place of the beasts and Jaffe scouts ahead but is speared by the beasts. Herb recovers him before fighting off the creatures. The leader of the beasts warns he has killed many of her people and he will kill all of them if need be. Borden sends Deena up with a message that he is a coward and Borden wants to fight the leader one on one using only an axe and knife
The leader takes up the challenge and comes out. After a frantic few minutes of fighting, Borden kills the leader. Borden declares himself the chief of the tribe and calls the other beasts to acknowledge him as the new leader
Months later, progress above ground is going well. Most of the colony is moving to live on the surface and the former tribe of the beasts is being integrated with the colony. Everyone agrees they are witnessing the rebirth of man's civilization.