Siblings Barbra and Johnny drive to a rural Pennsylvania cemetery to visit their father’s grave. In the cemetery, a strange man kills Johnny and viciously attacks Barbra as she attempts to take shelter in a distant farmhouse. After discovering the farmhouse resident half-eaten, she sees a multiplying number of strange ghouls led by the man in the cemetery. A man named Ben arrives and secures the farmhouse and drives away the ghouls. He also finds a lever-action-rifle and discovers the ghouls can be driven away by fire.
Barbra discovers the farmhouse has a cellar housing an angry couple, Harry and Helen Cooper, and their daughter, Karen, who all sought refuge after a group of the same monsters overturned their car and bit Karen, leaving her seriously ill. Tom and Judy, a teenage couple, previously arrived after hearing an emergency broadcast about a series of brutal killings. Tom aids Ben in securing the farmhouse while Harry protests and returns to the cellar. More ghouls besiege the farmhouse, increasing in numbers.
The occupants of the house listen as radio and television reports explain a mass wave of murder is occurring on the East Coast of the United States by an army of cannibalistic, reanimating corpses, and posses of armed men are patrolling the countryside to restore order. It also reports a heavy blow to the head (or fire, as Ben discovered) can stop the ghouls, and that various rescue centers are offering refuge and safety. The reports explain a possible theory from a scientist: the reanimations are due to a space probe’s radiation that exploded in Earth’s atmosphere while returning from Venus.
Ben devises a plan to obtain medical supplies for Karen and transport the group to a rescue center by refueling his truck. Ben, Tom, and Judy drive to a nearby gas pump with the ghouls in pursuit (partially wounded after Harry threw Molotov Cocktails at them). However, the truck catches on fire with Ben’s torch and explodes, killing Tom and Judy.
Ben beats Harry for nearly locking him outside in cowardice, and the remaining survivors attempt to find a way out. However, the ghouls break through the barricades as the remaining survivors face chaos; Harry is shot by Ben; Karen dies from her illness, reanimates, and begins to eat her father; Helen dies in the cellar after Karen stabs her with a masonry trowel; Barbra is taken away by the ghouls after attempting to secure the barricades.
Ben manages to take refuge in the cellar where he shoots Harry and Helen’s reanimate