Ben and Barbra are unaware that the farmhouse has a cellar, housing an angry married couple, Harry and Helen Cooper, along with their daughter Karen. They sought refuge after a group of the same monsters overturned their car. Tom and Judy, a teenage couple, arrived after hearing an emergency broadcast about a series of brutal murders. Karen has fallen seriously ill after being bitten by one of the monsters. They venture upstairs when Ben turns on a radio, while Barbra awakens from her stupor. Harry demands that everyone hide in the cellar, but Ben deems it a "deathtrap" and continues upstairs, to barricade the house with Tom's help.
Radio reports explain that a wave of mass murder is sweeping across the eastern United States. Ben finds a television, and they watch an emergency broadcaster report that the recently deceased have become reanimated and are consuming the flesh of the living. Experts, scientists, and the United States military fail to discover the cause, though one scientist suspects radioactive contamination from a space probe. It returned from Venus, and was deliberately exploded in the Earth's atmosphere when the radiation was detected.
Ben plans to obtain medical care for Karen when the reports list local rescue centers offering refuge and safety. Ben and Tom refuel Ben's truck while Harry hurls molotov cocktails from an upper window at the ghouls. Judy follows him, fearing for Tom's safety. Tom accidentally spills gasoline on the truck, setting it ablaze. Tom and Judy try to drive the truck away from the pump, but Judy is unable to free herself from its door, and the truck explodes, killing them both; the zombies promptly eat the charred remains.
Ben returns to the house but is locked out by Harry. Eventually forcing his way back in, Ben beats Harry, angered by his cowardice, while the zombies feed on the remains of Tom and Judy. A news report reveals that only a gunshot or heavy blow to the head can stop them, aside from setting the "reactivated bodies" on fire. It also reports that posses of armed men are patrolling the countryside to restore order.
The lights go out, and the zombies break through the barricades. Harry grabs Ben's rifle and threatens to shoot him. In the chaos, the two fight and Ben manages to wrestle the gun away and shoots Harry. Harry stumbles into the cellar and collapses next to Karen, mortally wounded. She has also died from her illness. The ghouls try to pull Helen and Barbra through the windows, but Helen frees herself. She returns to the refuge of the cellar to see Karen is reanimated and eating Harry's corpse. Helen is frozen in shock, and Karen stabs her to death with a masonry trowel. Barbra, seeing Johnny among the zombies, is carried away by the horde and devoured. As the zombies overrun the house, Ben fights off Karen and seals himself inside the cellar, where Harry and Helen are reanimating, and he is forced to shoot them.
The next morning, Ben is awakened by the posse's gunfire outside. Upon venturing upstairs, the posse mistake him for one of the ghouls and kill him with a shot to the forehead. Ben's body is thrown onto a pile of corpses which are set ablaze.
