At the funeral of an Old Man’s wife, mourners are gathered by an open grave, among them her husband (Bela Lugosi). Overhead, an airliner is heading toward Burbank, California. The pilot Jeff Trent (Gregory Walcott) and his co-pilot Danny (David De Mering) are blinded by a bright light and loud sound. They look outside and see a flying saucer. The pilots follow the saucer’s flight until it lands at the graveyard, where the funeral’s gravediggers are killed by a female zombie (Maila Nurmi).
At his home, lost in his thoughts of grief, the Old Man goes outside and (offscreen) steps in front of an oncoming car and is killed. Mourners at the Old Man’s funeral later discover the dead gravediggers. Inspector Daniel Clay (Tor Johnson) and other police officers arrive, but Clay goes off alone to continue his investigation.
Jeff Trent and his wife Paula (Mona McKinnon), who live near the graveyard, hear the sirens, and Jeff tells Paula about his saucer encounter, stating that the Army has since sworn him to secrecy. A powerful swooshing noise then knocks everyone to the ground at both the Trent residence and the nearby graveyard as a saucer lands. Police Inspector Clay then encounters the female zombie and the reanimated corpse of the Old Man, and he is killed by them.
Newspaper headlines continue to report saucer sightings over Hollywood Boulevard, while a trio of saucers flies over Los Angeles. In Washington, D.C. the military fire missiles at more saucers, while the Chief of Saucer Operations, Col. Thomas Edwards (Tom Keene), reveals that the government has been covering up saucer attacks. He mentions that one small town was annihilated, hinting at a secret history of other encounters.
The aliens return to their Space Station 7. Commander Eros (Dudley Manlove) informs their Ruler (John Breckinridge) that he has been unsuccessful in contacting Earth’s governments. To force their acknowledgment, Eros recommends implementing “Plan 9”, which will resurrect recently human dead by stimulating their pituitary and pineal glands. Meanwhile, Trent, about to leave on another flight, is concerned for his wife’s safety. He urges her to stay with her mother, but she insists on staying home. That night, the zombie Old Man rises and breaks into their house. He pursues Paula outside and is joined by his zombie wife and the zombie Inspector Clay. Paula barely escapes, but then collapses after her ordeal. All three zombies then return to Eros’ saucer.
At the Pentagon, Gen. Roberts (Lyle Talbot) informs Edwards that the government has been receiving alien messages. They explain that the aliens are trying to prevent humanity from eventually destroying the universe. The general dispatches Edwards to San Fernando, California, where most of the alien activity has occurred.
Though the Undead are under alien control, zombie Clay suddenly attacks and nearly strangles Eros. The Ruler closely examines zombie Clay and then orders the zombie Old Man destroyed in order to further frighten humanity. He then approves Eros’ Plan 9 to raise Undead armies and orders they march on the capitals of Earth.
In California the police and Edwards interview the Trents. Unknown to them, the flying saucer has returned to the graveyard. Officer Kelton (Paul Marco) encounters the zombie Old Man, who then chases him into the Trents’ yard, where the zombie Old Man is hit with Eros’ ray, causing his body to rapidly decompose. Not knowing what to make of this, the Trents, Edwards, and the police drive to the cemetery.
John Harper (Duke Moore) insists on leaving Paula in the car, but Paula refuses to stay alone. As a concession, Kelton stays behind. Eros and fellow alien Tanna (Joanna Lee) send zombie Clay to kidnap Paula and lure the other three to their saucer. Seeing the saucer’s glow off in the distance, Trent and the police head in that direction. At the car, Kelton is knocked out by zombie Clay. Upon awakening, Kelton calls for help, and Patrolman Larry (Carl Anthony) comes to his aid.
Eros allows Trent and the police to enter with their guns drawn. He then tells them human weapons development will inevitably lead to the discovery of “Solaronite”, a substance that has the effect of exploding “sunlight molecules”. Such an explosion would set off an uncontrollable chain reaction, destroying the entire universe. Eros now believes humans are too immature and stupid, so he intends to destroy mankind. Eros threatens to kill Paula if Trent and the police try to force him to go with them. Officers Kelton and Larry arrive, spotting zombie Clay holding the unconscious Paula not far from the saucer. Realizing their weapons are useless, they sneak up behind Clay and club him with a length of wood, knocking him out. Eros sees this and says Clay’s controlling ray has been shut off, which allows Paula to go free. A fight then breaks out between Eros and Jeff, but the saucer’s equipment is damaged during the struggle, starting a fire aboard. The humans quickly escape, and Tanna and the unconscious Eros fly away in their now burning saucer, which finally explodes, killing them both; their zombies quickly decompose to just skeletal remains inside their clothing.