Siblings Barbra and Johnny drive to a rural Pensilvania cemetery to place a cross with flowers on their father's grave. Johnny teases his sister, afraid of cemeteries: "They're coming to get you, Barbra!" Suddenly, a pale skinned man grabs Barbra, and Johnny rushes to save her. A fight occurs, and Johnny is ultimately overpowered and killed when he falls and hits his head on a tombstone. Barbra flees the scene, pursued by the man. Finding refuge in an empty house, she discovers a mutilated corpse at the top of the stairs. The home's telephone is offline and of no use (because her pursuer has just destroyed the cord connecting the house to the phone box on a power pole).
While attempting to flee the house, she encounters Ben, who brings her back into quarantine and later defends the house against straggling zombies. This is followed by an intense argument about Barbara's desire to search for Johnny. After a brief struggle, Barbra collapses in shock, and Ben carries her to a couch. Ben boards up the doors and windows from the inside, and takes a chair outside and scares off the attackers by setting it afire. Ben finds a rifle and a radio as Barbra lies catatonic.
The two are unaware that Harry and Helen Cooper, their daughter Karen, and young couple Tom and Judy have been hiding in the cellar until later. One of the attackers bit Karen earlier and she has fallen ill. Harry wants the group to barricade themselves in the cellar, but Ben argues that they would effectively be trapping themselves. Ben carries the argument, its opposition mounted exclusively by Harry Cooper, and the group cooperates to reinforce the main part of the house. The ghouls swarm around the house, searching for living human flesh.Radio reports explain that an epidemic of mass murder is sweeping across the eastern seaboard. Later, Ben discovers a television upstairs and the emergency broadcaster reveals that the creatures are consuming the flesh of their victims. A subsequent broadcast reports that the murders are being perpetrated by the recently deceased who have returned to life, dubbed 'ghouls'. Experts, scientists and military are not sure of the cause of the reanimation, but one scientist is certain that it is the result of radioactive contamination from a space probe that exploded in the Earth's atmosphere. A final 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.
Ben devises a plan to escape using the truck involving all of the men in the house. The truck is in need of fuel, so Ben and Tom go to an outside gas pump while Harry hurls Moltov cocktails from an upper window. On the way out the door, Judy fears for Tom's safety and chases after him. Upon arriving at the pump, Ben places a torch on the ground next to the truck. Tom loses control of the pump, splashing gasoline onto the torch, starting a fire that quickly engulfs the vehicle. Tom tries to drive the truck away from the gas pumps to avoid further damage, but when he goes to exit the truck, Judy gets stuck. Tom goes back into the truck to help her but before they can get out the truck explodes, killing them both. Ben runs back to the house to find that Harry has locked him out. He kicks the door open and, in a fury, fiercely beats Harry. The Cooper family, above, had been hiding in the cellar of the empty house where Ben was battling a horde of zombies.Some of the undead horde converges upon the truck and begin eating Tom and Judy's charred remains. Meanwhile, others try 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 wrestles it away from Harry and shoots him. Harry stumbles into the cellar, finds Karen dead, and dies.
Shortly after, Helen discovers that her daughter, Karen, has been transformed into one of the ghouls and is consuming her father's corpse. Karen repeatedly stabs her mother 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. She lets her guard down and is pulled into the horde and killed. Ben retreats into the cellar, locking the door behind him, ironically taking the course of action that Harry had recommended in the first place. The zombies, including Karen, Johnny and the man who attacked Barbra and Johnny at the start of the film, try to break in. Ben shoots the reanimated Harry and Helen Cooper, and waits for the morning rays.
In the morning, a posse approaches the house, hunting the remaining ghouls. Hearing the commotion, Ben ambles up the cellar stairs into the living room. Sheriff McClelland (George Kosana) spots him through a window, and, mistaking him for a zombie, has one of the posse members shoot him in the head, killing him. Still shots are shown of the posse members dragging Ben's body from the house and placing it on a pyre, next to the zombie that had attacked Barbra at the start of the film, as the closing credits roll. The film ends with a brief clip of the pyre burning.