Siblings Barbra and Johnny drive to a cemetery in rural Pennsylvania to visit their father's grave, where a pale man in a tattered suit kills Johnny and attacks Barbra. She flees to a nearby farmhouse but finds the resident's corpse lying half-eaten on the stairs. A growing horde of ghouls soon surround the house as a stranger, Ben, arrives and initially mistakes Barbra for the homeowner. After driving back several ghouls, he boards the windows and doors. While searching the home for supplies, he locates a lever-action rifle.
A nearly catatonic Barbra is surprised to find people already taking shelter in the home's cellar. Harry, his wife Helen, and their young daughter Karen fled there after a group of the same monsters overturned their car and bit Karen on the arm, leaving her seriously ill. A couple, Tom and Judy, took shelter after hearing an emergency broadcast about a series of brutal killings. Tom and Ben secure the farmhouse while Harry protests that it is unsafe aboveground before returning to the cellar. Ghouls continue to besiege the farmhouse in increasing numbers.
The refugees listen to radio and television reports of an army of cannibalistic corpses committing mass murder across the East Coast of the United States and of the posses of armed men patrolling the countryside to exterminate the living dead. Reports confirm that the ghouls can die again from heavy blows to the head, bullets to the brain, or being burned. Various rescue centers offer refuge and safety, and scientists theorize that radiation from an exploding space probe returning from Venus caused the reanimations.
Judith Ridley as Judy, near the gas pumpBen devises a plan to obtain medical supplies for Karen and transport the group to a rescue center by refueling his truck at a pump on the farm. Ben, Tom, and Judy drive there together, holding the ghouls off with torches and Molotov cocktails. However, the gas from the pump spills and causes the truck to catch fire and explode, killing Tom and Judy. Ben returns and breaks down the door when Harry does not let him in.
The remaining survivors attempt to figure a way out. They pause their discussion to watch the 3 a.m. news update until the power cuts out. The ghouls soon break through the doors and windows of the unlit home. In the chaos, Harry grabs Ben's gun but is disarmed and shot by Ben. Harry staggers down to the cellar and dies next to his daughter.
Karen dies from her injuries, becomes a ghoul, and eats her father's remains. She stabs her mother to death with a masonry trowel. Barbra tries to help Ben keep the ghouls out, but a reanimated Johnny drags her away. As the horde breaks in, Ben takes refuge in the cellar, where he shoots Harry's and Helen's ghouls.
In the morning, an armed posse arrives to dispatch the remaining ghouls. Awoken by their gunfire and sirens, Ben emerges from the cellar, but they shoot him, mistaking Ben for a ghoul. His body is thrown onto a bonfire and burned with the rest of the ghouls.
