Escape from the Planet of the Apes is a 1971 science fiction film starring Roddy McDowall, Kim Hunter, and Bradford Dillman. It is the second sequel to the Planet of the Apes movie of 1968, the first sequel being Beneath the Planet of the Apes (1970). This sequel is considered by critics to be one of the better of four sequels made. Its plot centers around many social issues of the day including race, social status, scientific experimentation on animals, nuclear war and government intrusion as well as women's rights.
In this film, actor Roddy McDowall returns to recreate the character of Cornelius which he created but did not portray in its entirety in the previous film. A new character of Dr. Milo is introduced played by actor Sal Mineo, who hoped his career would gain from the new project much as McDowall's career had from participating in the first film. Charlton Heston, star of the first film and supporting actor in the second, appears in this third installment only in two brief flashback sequences.
Escape from the Planet of the Apes begins by establishing that three apes (Cornelius, Zira, and Dr. Milo, played respectively by Roddy McDowall, Kim Hunter, and Sal Mineo) escaped the Earth's destruction. They have managed this by salvaging and repairing the astronaut Taylor's spaceship (which sank in the first movie) and piloting it through the shock wave of Earth's destruction sending the ship through a time warp back to 1973.
The apes arrive on Earth, splashing down on the Pacific coast. Marines haul the ship to the beach, and the apes remove their helmets. They are quickly transported to seclusion for examination and are later moved to a secluded area of the Los Angeles Zoo. They remain under the observation of two scientists, Stephanie (Natalie Trundy) and Lewis (Bradford Dillman). Both discover the apes' power of speech when Zira's impatience gets the better of her. Right afterwards, Milo is killed by a noncivilized gorilla who was agitated by an argument between the three chimpanzees. (Kim Hunter later said that Sal Mineo was happy to be killed off so early in the film because he hated the makeup process and was glad to be done with it.)
Meanwhile, a Presidential Commission has been formed to investigate the return of Taylor's spaceship and how the apes, which they already are aware are atypically intelligent, came to be aboard it. The apes then are brought before the Presidential Commission, where they publicly reveal their ability to speak, and are welcomed as guests. After the hearing, Cornelius and Zira secertly tell Stephanie and Lewis that they know about Taylor, what will happen to the human race, and the Earth's destruction. Stephanie and Lewis are shocked and surprised realizes about it and they decide to keep this quiet until the time is right.
The apes become celebrities, being lavished with presents and media attention. They are soon watched by a scientist, futuristic consultant Dr. Otto Hasslein (Eric Braeden), who discovers Zira is pregnant and fears for the future of the human race. He is determined to force the issue, gets Zira intoxicated on wine (which she knows as grape juice plus) to get information out of her and convinces the Commission to have the apes taken for proper questioning.
Both are questioned using numerous means of interrogation; one of Hasslein's assistants refers to the apes as "monkeys", stirring Cornelius anger. Hasslein defuses it, saying they simply want to know how apes rose in dominance over men. Cornelius tells what he knows, information that was not fully known to the general public of his time. Now, Hasslein has learned how the human race will eventually meet its downfall and be dominated by simians, which will eventually lead to Earth's destruction. However, there are still suspicions about how humans are treated by the future apes.
The suspicion had already been aroused by Zira's letting slip, during her first appearance before the newly-formed president commission, that she had dissected humans in the course of her work. Zira dismisses her slip of the tongue, therefore Hasslein orders Lewis to administer a truth serum on Zira, while Cornelius is taken to confinement quarters. Lewis warns Zira that the serum will have the same effect as the wine Hasslein used on her. As a result of the serum, Hasslein learns for himself that Zira examined and operated on humans in the future.
Zira is taken to join Cornelius in confinement while Hasslein takes his findings to the U.S. President (William Windom). An orderly brings food, and refers to the unborn child as a "little monkey"; Cornelius has heard enough of the epithet and accidentally renders a fatal injury to the orderly; he is stunned later to overhear that the boy died. Hasslein uses it as an illustration of the future danger the apes present and calls for the apes' execution. The president reluctantly orders that the unborn child's birth be terminated and that both be sterilized. Cornelius and Zira are outrage, however, they begin to see what Taylor saw in them as savages. Zira however, was glad to tell them, because she tired from running away from the truth. Cornelius and Zira escape and their running for their lives, Cornelius and Zira (assisted by Stephanie and Lewis) find shelter in a circus run by Señor Armando (Ricardo Montalbán), where an ape named Heloise has just had a baby. There Zira gives birth to a son, whom she names Milo.
Hasslein, knowing Zira will imminently give birth, orders a search of all circuses and zoos. As a result, Armando must send the apes away; Lewis grants Cornelius a pistol so the apes can die by their own hand... if it comes to that. The drama climaxes aboard a derelict ship in an abandoned ship yard. Hasslein tracks the apes down, and finds Zira resting with her infant. The fearful but ruthless Hasslein shoots Zira in cold blood after she refuses to hand over her infant and then proceeds to fire several shots into the infant; he is immediately shot to death by Cornelius, and falls overboard. After Cornelius kills Hasslein, he is shot by an unseen Marine Corps sniper (this unseen person is left mysterious to the viewer) and, as Stephanie and Lewis watch in horror, falls to the deck of the ship. Zira tosses her dead baby over the side of the ship before crawling to lie with her husband and dying by his side.
The survivors, however, are unaware of the real fate of the infant ape; Cornelius, Zira, and Armando switched babies before their final escape. Armando now watches over the infant Milo. The film ends by showing the baby ape Milo sitting in a cage, plaintively speaking the words "Mama? Mama?" with the voice of a human child.
Several elements of the plot are attempts to reconnect with the original book, Planet of the Apes, with human and ape roles switched. In the original book, the protagonist Ulysse Mérou came to the planet of the apes, was experimented on, and proved his intelligence. He then became a celebrity among the apes, and fathered an intelligent human child.