"Beneath the Planet of the Apes" is a 1970 science fiction film and the sequel to the original "Planet of the Apes." The story follows astronaut Brent, who searches for the missing Taylor, a character from the first film. He discovers a post-apocalyptic world where intelligent apes rule over humans, who are mute and oppressed. As Brent explores this new society, he encounters a hidden underground city inhabited by telepathic mutants. These mutants worship an atomic bomb, which poses a threat to both the apes and the remaining humans. The film explores themes of power, survival, and the consequences of nuclear war.