In the distant future, many years after a nuclear cataclysm has destroyed the earth's cities, a small community of apes and their human slaves live in peace. One of the apes, General Aldo, bristles at the orders of their leader, Caesar, that the humans be treated with respect, and refuses to take lessons from the human teacher, Abe. Caesar’s only son, Cornelius, is friendly with humans and wants to learn, mastering the writing of one of the ape society's most sacred affirmations, "Ape does not kill ape." Another human, MacDonald, who uses his skills as a mechanic to better society, is a confidant of Caesar and warns him that the future of earth is in jeopardy. Caesar does not believe this, even though MacDonald reveals that, when he was an assistant to the governor of the nearby destroyed city, Caesar's parents, Zira and Cornelius, predicted the end of their society in an interview that survives in the old city’s archives. Although MacDonald feels that the old city may still be too radioactive to enter, he asks Caesar to seek advice from Virgil, the wisest and most knowledgeable of the apes. Because Caesar's parents were killed by humans when he was a baby, he yearns to see them, if only on videotape, and decides to accompany MacDonald and Virgil to the city. After asking for a few weapons of self-defense from Mandemus, an elderly ape who scrupulously guards the armory, MacDonald, Caesar and Virgil walk to the city. Unknown to them, beneath the city there exists a group of humans governed by Kolp, who forcefully rules over his people. MacDonald guides Caesar and Virgil through the ruins to the archive, using a Geiger counter to measure the level of radioactivity. As they approach the archives, Mendez, one of Kolp's men, is able to follow their steps on television monitors that survived the war. Kolp, who recognizes MacDonald as his predecessor’s aide, also realizes who Caesar is and wonders if the ape wants to regain his lost kingdom. When Virgil, MacDonald and Caesar reach the archives, MacDonald reveals that the interviews with Cornelius and Zira are most likely stored within materials from the 1973 Presidential Commission. After MacDonald puts the tape into the player, Caesar emotionally watches the brief interview, in which his parents predict the future destruction of the earth. Virgil, however, says that there are actually many different futures, much like different lanes on a motorway. As they are talking, they suddenly notice that the surveillance cameras are moving, then hear shots ring out. Realizing that they have been identified by the remaining humans, the trio wind their way through the ruins, where mutated humans rest, and evade capture by Kolp's men. MacDonald is able to lead Virgil and Caesar above ground, after which they quickly return to their own village. Unable to pursue the intruders further, a mutant captain confesses his failure to his commander, Mendez, and Kolp. Although Mendez tries to convince Kolp that Caesar is wise and peaceful, Kolp will not listen and orders the captain to follow him. Back at the village, when Caesar calls his council together and reports on his mission to the destroyed city, Aldo becomes enraged that Caesar has invited some of the humans to listen, shouting "no humans at the council." Caesar answers by saying that the danger from the city humans concerns their humans as well, prompting Aldo and his followers to leave. Unknown to them, the meeting has been observed by the captain and his men, who return to the city and report that the apes live among vineyards and fields that produce food enough to feed the city humans. Overriding the objections of Mendez, Kolp orders his men to rebuild a school bus and other destroyed vehicles so that they can attack the apes. Meanwhile, Cornelius wanders off into the woods and hears Aldo and his followers chanting "guns" and "power." To have a better view of what is happening, Cornelius swings through the trees, which creates sounds that the other apes hear. Seeing Cornelius, Aldo orders the boy to come down, but when he instead climbs higher, Aldo uses his sword to hack through the tree's branches until Cornelius falls to the ground, calling for his mother, Lisa. Sensing something is wrong, Lisa runs into the woods and finds Cornelius unconscious and alone. The next morning, as the humans from the city prepare for their attack, apes and humans at the village sadly discuss Cornelius' grave condition. Although most believe that he simply fell from the tree, MacDonald notices that the branch from which Cornelius fell shows signs of being hacked off rather than an accidental break. Later, two apes see Kolp's men approaching and try to stop them but are killed by the flames from a bazooka. Meanwhile, as MacDonald relates to Caesar that Cornelius' fall was no accident, Aldo arrives to warn of the approaching humans. Seizing authority because Caesar will not leave Cornelius' bedside, Aldo declares martial law and orders that all of the human slaves be imprisoned within a stockade. Although Mandemus refuses to cooperate with Aldo's demand for all of the armory's weapons, he is soon overpowered by Aldo's men who chant "guns mean power; guns are power." Moments later, Cornelius briefly regains consciousness and tells his father that it was Aldo who hurt him. After Cornelius dies, the grief-stricken Caesar immediately leaves and lashes out at Aldo for his cruelty to the humans. Just then, Kolp and his men attack, creating chaos throughout the village. During the battle, Caesar is captured by Kolp, who taunts him for losing his kingdom, but a bomb thrown by Virgil enables Caesar to free himself. Caesar rallies his followers by saying "fight like apes," and the apes are able to rout the humans and force them to retreat toward the city. After Kolp and most of his men have been killed, Aldo returns to the village and, saying that he now is their leader, gives orders that all of the humans in the stockade be killed. When Aldo then threatens to kill Caesar for opposing him, Virgil speaks out, saying that apes do not kill apes—or child apes. Terrified as the other apes pursue him, Aldo climbs a high tree, trying to elude Caesar, who calls Aldo a murderer. As Aldo swings his sword at Caesar, Caesar grabs him arm in self-defense, causing Aldo to fall to his death. Caesar then asks Virgil if one death justifies another, but Virgil answers that only the future will tell. With Virgil and MacDonald's counsel, Caesar frees all of the humans and orders that all weapons be put back into the armory. Mandemus wants the weapons destroyed, but Caesar and Virgil say that they must wait until all danger has passed. Six hundred years later, The Lawgiver tells a group of human and ape children sitting beside a stature of Caesar that they are still waiting.