In 1960, a pilot testing an experimental rocket powered aircraft accidentally flies into the future and finds himself in a sealed city whose people suspect he is a spy from outside their walls, but who want to keep him to procreate with the ruler's daughter because the majority of the inhabitants are sterile.

Four astronauts returning from man's first mission to Mars enter a time warp and crash on a 26th Century Earth devastated by atomic war. At first unaware where they are, but finding the atmosphere safe to breathe, they start exploring and find themselves in a divided future where disfigured mutants living like cavemen inhabit the surface, while the normals live comfortably below the surface but are dying as a race from lack of natural water, air and sunlight.