One morning, high above the San Fernando Valley, commercial airline pilot Jeff Trent and his co-pilot Danny are aghast to see a flying saucer just outside their plane. While they report the sighting to the airport tower, the saucer secretly lands in a nearby cemetery, where two gravediggers are finishing the burial of an elderly man's young wife. Having heard a spooky noise the gravediggers are attempting to leave, when the corpse of the dead woman, Vampire Girl, rises from her grave and kills them. Soon after, Vampire Girl's widower dies of loneliness and is buried in a crypt. After the service, two mourners find the gravediggers' bodies and alert the police. Meanwhile, the elderly man is resurrected as well and becomes Ghoul Man, wandering the cemetery in a long, black cloak. While police inspector Clay looks for clues in the misty cemetery that night, Jeff, who lives nearby, explains to his wife Paula that after he spotted the flying saucer, the army debriefed Danny and him and forced them to promise to keep the sighting a secret. As Jeff expresses his frustration about keeping silent, a flying saucer whizzes by, the force of it pushing Jeff and Paula to the ground. Back at the cemetery, the saucer lands and Vampire Girl and Ghoul Man attack and kill Clay, whose bullets are useless against them. Lt. Johnny Harper and two patrolmen follow the sound of the gunfire and upon finding Clay's mutilated body, notice a foul smell in the air. Soon after, when flying saucer sightings in Hollywood and Washington, D.C. make headline news, the army sends Col. Edwards and his convoy on a secret mission to fire at the saucers, which are unharmed by the attack. The pilots of one saucer, Eros and Tanna, return to space station seven and report the incident to their Ruler, who is furious that Earth's government officials still refuse to acknowledge their existence. Fearing that the humans' nuclear weapons will result in the destruction of the whole universe, the Ruler has set into motion Plan Nine: Eros and Tanna have used their electrode guns to resurrect the dead and create a zombie army to control the living humans. Later, Jeff reluctantly leaves his wife alone to go to work, but, fearing for her safety, has the control tower call and check on her. Paula, who has gone to bed, assures the tower that she is fine, but as she hangs up, Ghoul Man breaks into her bedroom and sends her running from the house. Hysterical, Paula runs through the cemetery, where Vampire Girl and the now resurrected Clay lumber slowly after her. Paula faints from fright on a road, where a passing motorist saves her. When Harper arrives at the cemetery to investigate, he hears the spaceship lift off and discovers Clay's grave has been unearthed and his casket is empty. Meanwhile at the Pentagon, Gen. Roberts orders Edwards to investigate the San Fernando Valley cemetery incident and make contact with the aliens. Explaining that the army developed a computer system to decode their language, Roberts admits that the military has been in contact with the aliens for years. He then plays a recording of their last transmission in which the aliens announce that their technology is superior to that on Earth and accuse the earthlings of being stupid for assuming that they were only living beings in the universe. The aliens conclude that the earthlings' use of nuclear weapons has forced them to consider destroying the Earth's inhabitants in order to save the planet. Back at space station seven, Eros and Tanna report to the Ruler, who explains that as soon as they have enough walking dead to form a large troop, they will march on the powerful houses of government and demand that the earthlings accept the aliens' superiority. Back at the Trent house, while Edwards is interviewing Jeff and Paula, Ghoul Man suddenly attacks patrolman Kelton, who is knocked unconscious. When he then attempts to attack the others, a ray from the saucer renders Ghoul Man into a skeleton, a tactic the aliens hope will scare the humans into acknowledging their awesome power. After Kelton revives, Edwards rushes with Jeff and Harper to the cemetery and orders Kelton to remain at the car with Paula as they investigate the glowing light emanating from the spaceship. Soon after, Clay attacks Kelton, leaving him unconscious, and then carries Paula, who has fainted, toward the spaceship. Seeing the ship, Edwards, Jeff and Harper enter its opened hatch with guns drawn. Once the men are inside, Eros closes the hatch and points to a monitor showing Clay carrying Paula to the ship. Eros claims that his people have been contacting Earth for years, but humans have refused to acknowledge their existence. The earthlings' development of the Solaronite Bomb, which could destroy the sun, has put the rest of the universe, which is also dependent on the sun's existence, in jeopardy. An impassioned Tanna reiterates that it is not "mad" to kill earthlings if they are going to destroy every other planet through their ruthlessly irresponsible behavior. When Harper orders Eros and Tanna to go to the police station with him, Eros laughs and threatens to have Clay to kill Paula. Meanwhile, Kelton and another policeman find Clay and knock him down with a pipe, revive Paula and head for the ship. Back at the ship, a fistfight between Eros, Tanna and the earthlings ensues. While Edwards manages to open the ship's hatch, some equipment that was damaged in the fight causes a fire to start onboard. Edwards, Harper and Jeff flee just as the burning ship takes off into the night sky and explodes. Instantaneously, Clay's body turns to bones, the ship having lost control of the ghouls and their mission on earth.