 Three twentieth century astronauts travel through a time warp and crash on Earth in 3085 A.D.. One of the astronauts is killed in the impact, and the two survivors, Alan Virdon and Pete Burke, find that they have returned to an Earth where their loved ones are long dead, where technological civilization has fallen, and where humanity is subjugated by intelligent, talking simians who live in jungle cities and preside over pastoral hinterlands. The two astronauts are captured by horse-riding gorillas (the ape army) and taken before an orangutan tribunal. They are deemed a threat to ape security and sentenced to death. The two condemned men are visited in their cell by a curious chimpanzee named Galen, who is fascinated by their accounts of an advanced human civilization centuries past. After Galen accidentally kills a gorilla and is charged with murder, Virdon, Burke, and Galen all escape the ape city and are fugitives hunted by a determined gorilla named Urko. Virdon manages to salvage a computer disk from the downed spaceship before it is destroyed by the gorillas, and the trio s travels take them to the earthquake-prone remains of a human city, where they are cornered by Urko s troops.