Astronauts Alan Virdon and Peter Burke leave Earth on a deep-space mission in 1985. They inadvertently pass through a timewarp and return to Earth, but find that they have jumped 1,100 years into the future. Apes have now evolved intelligence and speech and are the predominant lifeform, keeping the uncivilized humans as slaves. The apes know that human kind almost wiped itself out in nuclear war and are afraid of any technology more sophisticated than guns.