Beneath the Planet of the Apes is not remotely the equal of its predecessor, falling lower in many respects. But nonetheless it is a sturdy enough sci-fi adventure movie with some keen ideas giving it a power its narrative doesn't really fully develop nor support.
The story picks up of course right at the epic finale of the first movie and we follow Taylor and Nova as they attempt to find someplace to live in this ruined Earth. They encounter though weird weather effects and Taylor disappears into a rockface leaving Nova alone to seek out Zira and Cornelius.
Meanwhile another spaceship has landed, this one with two astronauts only one of whom survives, a man named Brent. Brent finds Nova and connects her to Taylor and the duo head to Ape City where General Ursus is trying to stir up a crusade into the Forbidden Zone to ostensibly find more food and the secrets which he suspects are there as evidenced by the mysterious Taylor.
Brent is horrified but finds more solace and help from Zira and Cornelius but still he and Nova are captured though it doesn't last long. They are chased into the Forbidden Zone where he discovers he is on Earth when he finds the ruins of the New York City subway system. He also finds mutants who live under the Earth in this ruined city and worship a deadly atomic doomsday weapon.
Taylor is found and he and Brent work together briefly to forestall the mind-reading mutants who finds themselves overwhelmed by the ferocious Ape army despite assaulting the gorillas with terrifying illusions.
Most of the cast is killed before Taylor ignites the doomsday weapon and ends the planet.
But as we know that's not the end of the story.
Beneath The Planet of the Apes is my favorite title among the many of the series, it's ripe with mystery and symbolism. The story literally plumbs the depths of the ruined world and also attempts to get under what drives these characters and all of us to ultimate doom. That's a grand goal, but alas the movie falls far short.
To begin with it I'd class this movie, and most of the sequels which followed as a "B" movie. The original was "A" all the way, a first-class serious entertainment. This sequel like most sequels is too content to merely recreate variations on the beats of the original.
To its credit the introduction of the mutant culture beneath NYC does offer up new territory, but some of that clashes a bit with what we've already learned. I've always found the creepy mutants of this story a bit too slick, too smooth. The production as a whole lacks the singular imagery of the original and feels all too often like a made-for-TV effort, especially in regard to action sequences.
James Fanciscus has a thankless role, most of the time he's just a doppleganger for Taylor who is hidden away most of the movie and he himself is given little development. The story depends a great deal on coincidence to make the plot work and sometimes too much so when more reasonable solutions seemed available. Overall the movie feels like it was put together quickly.
It did well and despite the seeming end of the planet, there would be others. More to come.