Beneath the ruins of civilization lies the Forbidden Zone, a mysterious land where humanity's darkest secrets are buried. As astronaut Brent (played by James Franciscus) embarks on a perilous journey to find his lost comrade, Taylor, he encounters a society ruled by intelligent apes. Teaming up with the enigmatic Nova (played by Linda Harrison), Brent delves deeper into the forbidden territory, only to discover a shocking truth that could change the fate of both humans and apes forever.