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. Meanwhile ape leader Dr. Zaius learns of the presence of the spacemen and wants them captured and questioned, much to the chagrin of General Urko, who wishes them dead. To protect his interests, Zaius sends his young assistant Galen with Urko to retrieve the humans. The apes capture the humans and they are taken before the council. Zaius orders them confined for questioning, but Urko conspires to free the humans, and then kill them as escaping prisoners. However, Galen learns of this and foils Urko's plan, allowing the humans to escape. Galen is arrested and accused of murdering one of the guards. The humans must rescue Galen before retrieving a magnetic disc, which could hold the key to returning to their time.
Burke, Virdon and Galen come across two humans fighting and get involved, but lose the magnetic disc. To recover it, they must approach the nearby village, where the ape prefect pits humans in a series of gladiatorial games.
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.
Burke and Virdon have to seek the help of a gorilla farmer and his family when Galen falls sick.
Burke and Virdon are helped by a young woman and a young boy while searching for an underground computer in a ruined city, but their plans go awry when Alan is captured and Urko uses the boy to get information from the astronaut.
An ape who runs a fishing business plans to use Virdon and Burke as slaves after he captures them.
Galen must use all his charm to try and persuade his ex-girlfriend, a female ape surgeon named Kira, to operate on Virdon using a forbidden human anatomy book, after the astronaut is shot.
When the guys try to track down the apes who are framing humans for crimes in a small community, Fauna, a blind female ape, falls in love with Burke while believing him to be a chimpanzee.
Virdon decides to take part in a dangerous horse race even though he runs the risk of being captured by Urko.
Burke undergoes a horrific interrogation after being captured whilst Virdon and Galen mount a rescue attempt.
Aboro, a despot, is making community life a misery; Burke, Virdon, and Galen decide to rob him of his powers.
Thanks to their advanced medical knowledge, Burke and Virdon are able to help a village struck with malaria, but risk discovery.
Burke and Virdon are captured by a bunch of humans determined to hand them over to the Apes.
Burke and Virdon join forces with Leuric, a human attempting to fly by building himself a hang glider.
