Zira, Cornelius and Milo escape from the future earth before it is ended at the end of the second film, and they find that they have landed on Earth in 1973 by hitting the same time warp encountered by Taylor and other earth astronauts.
At first all are treated as animals and put in a zoo until Zira shocks them by actually speaking. Dr. Milo is accidentally killed by a gorilla, and soon Zira and Cornelius become honored guests. This all changes when the government discovers that Zira is pregnant and the her baby might be the one who leads a revolution to overthrow the human race.
This is one of the best of the series and even today can really make you think. Bradford Dillman and Natalie Trundy are two scientists that befriend the two fugitive apes. Kim Hunter and Roddy McDowell are Zira and Cornelius respectively. I really recommend this entry.
The ending is a sad one, but fitting and open for the fourth segment. The rest of the cast includes William Windom, Sal Mineo as Milo, Eric Braeden, Jason Evers, Albert Salmi, Asa Maynor, and John Randolph.