Astronauts Taylor, Landon and Dodge are in deep hibernation when their spaceship crashes into a lake on an unknown planet after a light-speed voyage. They discover their fourth crew mate, Stewart, dead due to a malfunction. The three abandon their ship when it starts sinking; Taylor remains on board long enough to see that the date is November 25, 3978, two thousand and six years after their departure in 1972.

The astronauts set off through a desolate wasteland and discover an oasis in the desert, ignoring eerie scarecrow-like figures around the edge. Their clothes are stolen while they take a swim. The astronauts pursue the thieves, finding their clothes torn to shreds and their supplies pillaged as the perpetrators, a group of mute primitive humans, raid a cornfield. Taylor is shot in the throat and captured by armed gorillas, along with the primitive humans. Dodge is killed and Landon rendered unconscious in the chaos. Taylor is taken to Ape City where he is saved after a blood transfusion administered by two chimpanzees: animal psychologist Zira and surgeon Galen. However, Taylor's throat injury renders him temporarily unable to speak.

Taylor is placed with one of the captive primitive humans, whom he later names Nova. He observes the enhanced society of talking apes and in a strict caste system: the gorillas serving as military forces and labourers; the orangutans overseeing the affairs of government and religion; and intellectual chimpanzees being mostly scientists and doctors. While their society is a theocracy similar to the beginnings of the human Industrial Era, the apes consider the primitive humans as vermin. Humans are hunted, either killed outright, enslaved, or used in scientific experiments. Taylor convinces Zira of his intelligence as she and her fianc� Cornelius, an archaeologist, take an interest in him. Dr. Zaius, their orangutan superior, learns of this and arranges for Taylor to be castrated. Taylor escapes and finds Dodge's stuffed corpse on display in a museum. When Taylor is recaptured, he suddenly regains his speaking abilities and much to the amazement of the onlookers, he shouts: "Take your stinking paws off me, you damn dirty ape!"