At the end of 1970's Beneath the Planet of the Apes, the first sequel in the original five-movie series, friendly chimpanzees Cornelius and Zira somehow managed to avoid the nuclear bomb that wiped out the rest of the cast. So, here they were, a year later in Escape From the Planet of the Apes, on Earth in the year 1973 – thanks to a convoluted time-warp explanation that makes much more sense plot-wise if you don't think too hard about it.

The Apes franchise was booming in the early '70s. The third movie was greenlighted even before the second one hit theaters. And it all quickly came together, with screenwriter Paul Dehn – who was behind Beneath the Planet of the Apes, as well as the next two movies in the series – throwing together a script that was lighter in tone than its predecessor, taking satirical cues from Pierre Boulle's 1963 novel.

The film itself (originally titled Secret of the Planet of the Apes in its screenplay form) was shot in six weeks by Don Taylor, an actor who starred in '50s movies like Father's Little Dividend and Stalag 17 but had steered toward TV direction in the '60s. For his first theatrical feature, he was given a small budget to work with.

Fortunately, the script included more humans than apes this time around because the story was set in contemporary times. Only Cornelius (a returning Roddy McDowall), Zira (Kim Hunter for the final time) and a new character, Dr. Milo (played by Sal Mineo), required the elaborate simian makeup that defined the previous two outings. That meant the movie couldn't rely on a bunch of talking apes when the plot slowed down.

Watch 'Escape From the Planet of the Apes' Trailer

And despite a somewhat abstruse time-travel premise that sets this entire movie in motion, the story is one of the series' sharpest, interweaving religious and civil-rights allegories among the plights stacked against Cornelius, Zira and Milo. It's not very subtle, but it's not really meant to be. Still, for a film franchise that sprouted into increasingly more juvenile branches, it's relatively deep stuff.

After the chimps' surprise arrival is explained away, Escape From the Planet of the Apes moves into its main storyline, as the time travelers first become celebrities and then the cause of concern when it's discovered Zira is pregnant and had dissected humans as part of her job back in her own time.

It's not long before an evil scientist takes his discoveries to the president, and Cornelius and Zira are on the run, aided by a pair of friendly doctors (just as the chimps had befriended the wayward astronauts in the first two films). It all leads to a downer of an ending spiked with a dash of hope, as a protective circus owner (played by Ricardo Montalban) ends up with the ape couple's talking baby – a direct line to the next movie in the series, 1972's Conquest of the Planet of the Apes.

Like its two predecessors, Escape From the Planet of the Apes topped the box office the week of its opening on May 26, 1971. Its mix of action, humor and social message also made it the best of the '70s sequels. Setting it in a new world bustling with fresh faces and locations certainly helped, too. So did the circling back to the first Planet of the Apes movie from 1968 by setting in motion the events that lead to the inevitable destruction of man and rise of the apes.

This third movie remains a pivotal part of the saga, even though details big and small would get muddled and rewritten as more sequels, TV shows, comic books and big-screen relaunches were commissioned over the years. It's basically the first chapter, the Adam and Eve origin of two apes and how their advent eventually and inadvertently started a planet-shaking revolution.


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