After defusing followers of Aldo who attacked a human teacher for saying "No" to apes, Caesar ponders if his own parents could have taught him how to make things better. MacDonald, Caesar's human assistant and the younger brother of MacDonald (from "Conquest of the Planet of the Apes") reveals to Caesar that his brother told him of archived footage of Cornelius and Zira within the underground, now radioactive ruins of what is known as the Forbidden City from the last film. Caesar travels with MacDonald and his orangutan advisor Virgil to the Forbidden City to find the archives.