In this sequel to 'Planet of the Apes', astronaut Brent (James Franciscus) is on a special mission to rescue George Taylor (Charlton Heston). Teaming up with Taylor's mute former comapnion, Nova (Linda Harrison), Brent travels to the ape village where he was imprisoned. After meeting Dr Zira (Kim Hunter), Brent learns that Taylor was last seen in the Forbidden Zone. He sets off in pursuit, and discovers that his colleague has been taken prisoner by an underground society of telepathic mutant humans who worship an atomic warhead. Meanwhile, Dr Zaius (Maurice Evans) has joined a gorilla expedition to investigate the strange goings on in the Zone. Followed by 'Escape from the Planet of the Apes'.