A carnival owner comes across small aliens who are spraying crops so that humans who eat the food will produce midgets so they won't have a size advantage when they invade, but he fools them into leaving Earth by claiming that the food is only producing small children ten percent of the time and producing giants the rest. He displays his circus giant to them as proof and they buy into his lie and leave.
Human colonists are forced off Mars and so attempt to return to Earth only to be rejected by the cavemen remnants left after atomic war. They go into orbit around Earth and wait for the cavemen to evolve to the point that they will no longer be considered another race.
Murdock invents a serum that will preserve his brain even though his body appears dead because he hopes to avoid atomic war that is impending. Peace breaks out and scientific advances occur that allow immortality, but Murdock lies in a coffin appearing dead but really just thinking, immobile.