Bickering siblings Johnny and Barbra are traveling by car to a rural cemetery, where they visit their father's grave. They are approached by a pale-faced man who stumbles toward them and attacks Barbra. Johnny pulls the man off of Barbra and struggles with him, but is knocked unconscious and possibly dead after tripping and hitting his head violently on the edge of a gravestone. The man then pursues Barbra back to the car, but Barbra cannot start it because the keys are in Johnny's pocket. She takes the car out of gear and it begins to drift away on its own, but she accidentally steers it into a tree. She abandons the car and runs down a roadway to a nearby farmhouse, with the man still pursuing her. She discovers the house seemingly deserted, and the phone is out of order. Her attacker stumbles around the outside of the house looking for her, and is joined by several others. They all seem to be in a kind of trance, behaving in an animalistic way. Exploring the house further, Barbra makes a gruesome find at the top of the stairs: a human body that seems to have been partially devoured by something.
In a panic and attempting to flee the house, Barbra is intercepted by Ben, who arrives in a pickup truck and attacks the mysterious figures with a tire iron. Barbra is further driven into hysteria when she sees Ben violently smashing the skulls of the strange men who keep trying to get into the house. Ben urges her into action and the two of them begin boarding up the doors and windows from the inside with dismantled furniture and scraps of wood. They awkwardly trade their stories; Ben seems to be a drifter who was passing through the area when suddenly a wave of unexplained violence began unfolding. He tells Barbra about a scene of mayhem that he encountered at a diner, and Barbra tells him about the incident with Johnny in the cemetery. When Barbra becomes hysterical and wants to go out after Johnny, she strikes Ben and Ben hits her in the face. Barbra passes out in shock.
Ben goes upstairs and finds a rifle and a radio as Barbra lies incapacitated on a couch in the living room listening to the radio report. Emergency broadcasters tell stories of widespread violence and mayhem being committed by people who seem to be in a 'trance'. Suddenly, Barbra is startled when the cellar door opens and people emerge from the basement. Ben is attracted by her screams and they confront the newcomers. An older man introduces himself as Harry Cooper, and the younger man is named Tom. Harry says that he has his wife, Helen, and his daughter, Karen, in the basement as well. Karen has been hurt and cannot be moved. Tom has a girlfriend named Judy, also in the cellar hiding.
Immediately the group begins bickering. Ben is furious with Tom and Harry for not coming out earlier to help him barricade the house. Harry is an irrational man who insists that they all barricade themselves in the cellar and wait for help. Ben refuses, saying that if their attackers ever got into the cellar, it would be the end of all of them, as there is only one entrance. Harry angrily retreats to the cellar with Helen and Karen, and Judy comes upstairs to be with the rest of the group.
Radio reports explain that an epidemic of mass murder is sweeping across the eastern seaboard of the United States. Later, Ben discovers a television and the emergency broadcaster reveals that the murderers are recently dead human beings who have returned to life and who are consuming their victims' flesh. Experts including scientists and military generals are not sure of the cause of the reanimation, but one scientist is certain that it is the result of radiation emanating from a Venus space probe that exploded in the Earth's atmosphere. The report instructs that a gunshot or heavy blow to the head will stop the "ghouls" and that posses of armed men are patrolling the countryside to restore order.
The broadcast provides a constantly scrolling list of local towns that contain "rescue stations" to provide citizens with protection and necessities. Ben notices a nearby town called Willard and devises a plan to escape using his truck, but it needs refueling. He exits the house armed with the rifle and a torch. Tom and Judy offer assistance, but when they arrive at a fuel pump near the house, Tom carelessly splashes gasoline on the torch, starting a grass fire that quickly spreads to cover the truck. The truck explodes with Tom and Judy inside. Ben runs back to the house to find that Harry locked him out. He kicks the door open and forces his way inside, and after Harry helps him board up the door again, he punches Harry repeatedly. Some of the living dead begin eating Tom and Judy's charred remains.
Another broadcast comes on the television, showing a local news reporter (Bill Cardille) interviewing a local sheriff (George Kosana) about the search and rescue operations that are underway in the area. Another news report indicates that the levels of the "mysterious radiation" in the area have been increasing, suggesting that the phenomenon is going to become even more widespread than it already is, but also that the situation is going to be under control soon. At that moment, the house goes dark when the area loses power. Perhaps triggered by the darkness, the ghouls surrounding the house begin to attack, attempting to break through the doors and windows of the house. Ben manages to hold them back, but drops his rifle. Harry seizes the fallen rifle and turns it on Ben, who wrests it away from Harry and then shoots him. Harry stumbles into the cellar and dies, approaching Karen's seemingly lifeless body.
Helen also attempts to hold off the zombies, whose great numbers are beginning to overwhelm the barricades over the windows and doors. Barbra suddenly throws herself into the battle, and Helen escapes back into the cellar, where she discovers that her daughter has been transformed into one of the living dead and is consuming part of Harry's corpse. Karen stabs her mother repeatedly with a cement trowel, killing her, before going upstairs. Meanwhile, the undead finally break into the house and Barbra sees her brother Johnny among them. The resultant shock causes her to lower her defenses and she is carried away into the zombie horde. Ben retreats into the cellar, locking the door behind him (which, ironically, was Harry's plan all along). He shoots the reanimated Harry and Helen Cooper.
In the morning, a posse approaches the house and proceeds to kill the remaining zombies. Hearing the commotion, Ben cautiously goes up the cellar stairs into the living room, but is shot in the head by an overzealous posse member who mistakes him for a zombie. His body is carried from the house and burned with the zombie corpses, including that of the man who chased Barbara at the start of the film.
- Duane Jones as Ben
- Judith O'Dea as Barbara
- Karl Hardman as Harry Cooper
- Marilyn Eastman as Helen Cooper
- Keith Wayne as Tom
- Judith Ridley as Judy
- Kyra Schon as Karen Cooper
- Charles Craig as Newscaster/Zombie
- S. William Hinzman as Cemetery Zombie
- George Kosana as Sheriff McClelland
- Frank Doak as Scientist
- Bill Cardille as Field Reporter
- A.C. McDonald as Zombie/Posse member
- Samuel R. Solito as Zombie/Posse Member
- Mark Ricci as Washington Scientist