Beneath the Planet of the Apes is a 1970 science-fiction film directed by Ted Post, and the first of four sequels to 1968's Planet of the Apes. The film stars James Franciscus and Kim Hunter, and features Charlton Heston in a supporting role.
The film story begins at the conclusion of Planet of the Apes, with the discussion between Dr. Zaius and Taylor about mankind and the quotation from the apes' sacred scrolls read by Cornelius (Roddy McDowall via scenes from the original POTA):
The opening credits are shown with Taylor (Charlton Heston) and Nova (Linda Harrison) riding through the desert of the "Forbidden Zone". Taylor investigates a specific area and suddenly disappeared in front of Nova's eyes.
Elsewhere in the Forbidden Zone is a severely damaged spacecraft which has crash-landed. It contains two survivors: an astronaut named Brent (James Franciscus) and his skipper Maddox (Tod Andrews). Though the skipper succumbs to his injuries and dies soon after, Brent believes it is 3955 AD. After burying his skipper, Brent is approached by Nova who is on horseback and wearing Taylor's metal I.D. tag. Hoping that Taylor may still be alive, Brent mounts the horse behind her and they ride out of the desert into the greener, cultivated area outside of Ape City.
They sneak to an amphitheater filled with cheering apes. Addressing the crowd is General Ursus (James Gregory), leader of the Ape Army, who is calling for the total extermination of all humans. The orangutans and chimpanzees in the crowd are silent, not agreeing with the statement. Ursus wants the Apes to invade the Forbidden Zone, conquer it, and use it as a potential food source.
After the rally, Dr. Zaius (Maurice Evans) and General Ursus are in the steam baths as they discuss the impending invasion with Dr. Zaius conveying his misgivings about fighting an unknown and potentially dangerous enemy. Ursus says, "Now we invade or we starve. It's as simple as that." "And as dangerous.", Zaius replies. When Ursus asks, "What is more dangerous than famine, doctor?", Zaius answers "The unknown."
While leaving the amphitheater, Brent is wounded by a patrolling gorilla trooper. Nova takes him to the home of Cornelius (David Watson) and Zira (Kim Hunter) who explain the situation to Brent and treat his wound. When Dr. Zaius arrives, Brent and Nova hide and overhear how Zaius protected Cornelius and Zira from charges of heresy and treason months before, but now scolds Zira for her behavior during the meeting, wherein she remained seated when everyone else stood in applause. He informs them that he will be joining Ursus on the invasion of the Forbidden Zone. While he is away, he asks for reassurances that they will stay out of trouble.
Brent and Nova quickly leave Ape City, but are immediately captured by a gorilla patrol. They are taken back to Ape City, passing squads of gorilla soldiers going through military exercises using humans for targets. At the compound, they are spotted by Zira who feigns scientific interest to save them. However, General Ursus has authority over them. As they are loaded back into the wagon, Zira pretends to lock the door but leaves it unlocked, enabling them to escape.
After escaping, Brent and Nova hide in an unnatural-looking cave which Brent soon recognizes was formerly Queensboro Plaza station. Overwrought, he wonders aloud what could have happened to destroy the world he knew. Brent and Nova go deeper into the tunnels, eventually following a humming sound. Brent hears voices that order him to kill Nova, resisting them, he enters the remains of St. Patrick's Cathedral, and finds a person inside, kneeling before the high altar. However, the object of worship fills him with horror - an intact nuclear intercontinental ballistic missile.
In the ruins of Grand Central Terminal, the city rulers Albina (Natalie Trundy), Caspay (Jeff Corey), Mendez (Paul Richards), Ongaro (Don Pedro Colley), and Verger (Gregory Sierra) barage Brent with questions asked telepathically, mentally torturing him when he is evasive. When it is apparent that he can not handle their telepathic communication, their leader instructs them to use verbal questioning. When they torture Nova, Brent confirms their worst fears; “The Apes are marching on your city!” Other than their “Divine Bomb”, the mutants’ only defenses are telepathic illusions.
In the Forbidden Zone, the ape army comes upon the horrible sight of their gorilla scouts crucified on inverted crosses, engulfed in flames. General Ursus is outraged and then frightened when a monolithic statue of their Lawgiver appears over them and begins to bleed. Instead of instilling fear, Dr. Zaius is incensed at the sight but recognizes it as an illusion, and charges through it, confirming its falsehood. Ursus orders the army to continue their advance.
With the failure of their illusion to dissuade the apes, the mutants have no choice but to prepare to detonate the “Divine Bomb.” The mutants hold a worship service in the cathedral, Brent and Nova are given robes to wear and attend. The congregation sings a corrupted version of the Anglican hymn “All Things Bright and Beautiful”, praising “the Bomb Almighty,” and in unison remove masks which have concealed their true appearance. Exposed to centuries of radioactive fallout, the mutants are skinless and horribly scarred.
Afterward, Brent is separated from Nova and put in a jail cell with Taylor. Ongaro explains their practice of getting their enemies to kill each other. Under his telepathic control, Taylor and Brent fight each other. Hearing the sound of the fighting, Nova escapes her guard and runs to the cell. She cries out “Tay-lor!” The sound of her voice breaks the mutant’s concentration, freeing Brent and Taylor from his control and they kill him. While Taylor is patching up Brent's wounds, Brent had described the missile to Taylor in the cell which from the "ΑΩ" (Alpha and Omega) markings. Taylor recognized as the "doomsday bomb" and that if it is launched, it will destroy the entire planet. At this time, the apes have entered the tunnels of the city and starts killing off the mutants. One of them manages to kill Nova before being killed by Brent and Taylor.
Using a battering ram, the apes force their way into St. Patrick’s Cathedral to be confronted by Méndez (Paul Richards), the leader of the mutants. The missile rises into launch position, and Taylor and Brent arrive just in time to see Méndez gunned down by the gorillas before he can fire it. The gorillas start to pull down the missile with ropes.
Brent and Taylor attempt to stop General Ursus from accidentally setting off the weapon, but Taylor is shot. Seeing this, Brent goes into a rage. Coming out into the open, he starts killing gorillas, beginning with General Ursus himself.
As this is going on, Dr. Zaius confronts Taylor. The mortally wounded man pleads with Dr. Zaius for help and states that the end of the world is near. Dr. Zaius contemptuously refuses and quotes "You ask me to help you?! Man is evil, capable of nothing but destruction!" With this remark, Brent's rifle empties and the gorillas kill him in a barrage of gunfire. With his last words, "You bloody bastard...", Taylor dies and his outstretched hand falls on the control switch that triggers the bomb. As that final scene whites out, the film ends with a narration (spoken by veteran voice actor Paul Frees):