Astronauts Alan Virdon and Peter Burke crash land on a strange planet. After being rescued by a friendly human, Virdon and Burke discover this planet is ruled by intelligent apes. To their horror, they discover that they are back on Earth in the year 3085.

In a ruined city, Burke and Urko are trapped underground and must reluctantly work together to escape, while Alan and Galen must deal with Urko's gorilla patrol in the streets above.