In the film, set in a world that has embraced ape slavery, Caesar (McDowall), the son of the late simians Cornelius and Zira, surfaces out of hiding from the authorities and prepares for a rebellion against humanity.
Following a North American pandemic from a space-borne disease that wiped out all dogs and cats in 1983, the government has become a series of Schutzstaffel-patterned police states that took chimpanzees, gorillas, and orangutans as pets before establishing a culture based on ape slave labor.
Caesar is then put to work by Breck's chief aide MacDonald, whose African American heritage allows him to sympathize with the apes to the disgust of his boss.
While setting the city on fire, Caesar and the rest of the apes proceed to the command center, killing most of the riot police that attempt to stop them in the process.
Don Murray suggested to Thompson his wardrobe with a black turtleneck sweater, and rehearsed his scenes after translating his dialogue into German "to get this kind of severe feeling of the Nazis".
Screenwriter Paul Dehn wrote the film incorporating references to the racial conflicts in North America during the early 1970s, and Thompson further highlighted by shooting some scenes in a manner similar to a news broadcast.
The primary location was Century City, Los Angeles, that had previously been part of the 20th Century-Fox backlot and translated well the bleak future with monochromatic buildings in a sterile ultramodern style.
The film's script and novelization describes a nighttime pre-title scene where police on night patrol shoot an escaping ape and discover that his body is covered with welts and bruises as evidence of severe abuse (in a later scene Governor Breck refers to the "ape that physically assaulted his master," thereby prompting MacDonald to report that the escape must have been the result of severe mistreatment).
I have a complete chronology of the time circle mapped out, and when I start a new script, I check every supposition I make against the chart to see if it is correct to use it...While I was out there [in California], Arthur Jacobs said he thought this would be the last so I fitted it together so that it fitted in with the beginning of Apes One, so that the wheel had come full circle and one could stop there quite happily, I think?Howard Thompson of The New York Times wrote that "J. Lee Thompson's direction furiously propels the action in a compact chromium-and-glass setting—and wait till you see that last battle royal.
"[10] Arthur Murphy of Variety wrote, "McDowall is extremely good as usual in simian character, and Thompson's staging keeps the pace very lively.
"[11] Gene Siskel of the Chicago Tribune gave the film 2.5 stars out of four, calling it "excellent in the first half hour," but found "the concluding action sequences run on too long without any original slashing, maiming, or setting on fire.
It is a simple but powerful premise, thoroughly developed with a good balance between dialog and action by Dehn and splendidly directed by J. Lee Thompson.
"[13] Clyde Jeavons of The Monthly Film Bulletin wrote, "This comic-book adventure is a far cry from the provocative Pierre Boulle vision so impressively realised by Franklin Schaffner four films ago; and in spite of some crude allegorical pretensions, it can't really be considered seriously as more than another excuse by APJAC to get maximum wear out of an expensive set of costumes.
The critical consensus reads: "Conquest of the Planet of the Apes is as angry and relevant as any of its predecessors, but budget constraints and a stale script rob this revolution of the scope it requires.