Plot
In New York City, during a séance held in the apartment of medium Theresa, Mary Woodhouse experiences a vision of a priest, Father Thomas, hanging himself in a cemetery of a village called Dunwich. Mary breaks the circle and collapses to the floor when the images overwhelm her. The group presumes Mary is dead and calls the police, who suspect foul play. Theresa warns the police chief of an imminent evil. Journalist Peter Bell begins to investigate Mary's death and visits her grave as she is about to be buried. However, she is still alive, and Peter saves her after hearing her cries. Peter and Mary visit Theresa, who says that according to the ancient book of Enoch, the events Mary witnessed in her visions presage the eruption of the living dead into our world. Father Thomas' death has opened the gates of Hell, and the invasion will commence on the upcoming All Saints Day.
In Dunwich, Bob, a young vagrant, visits an abandoned house but flees after seeing a carcass. Across town, Gerry, a psychiatrist, is in consultation with Sandra, a neurotic patient. Emily Robbins, his 19-year-old girlfriend and personal assistant, later tells him that she will meet with Bob, whom she has been trying to help. That evening, Emily finds Bob at a derelict garage exhibiting unusual behavior. Father Thomas then appears as Bob runs away, smothering Emily to death with a maggot-covered hand. The next morning, Emily's body is found. Emily's father tells the sheriff and Gerry of his suspicions about Bob due to the latter's history of crime. Meanwhile, Peter and Mary leave New York and embark upon their search for Dunwich.
That evening, Bob returns to the deserted house and has a vision of Father Thomas. After Emily's funeral, her younger brother John-John sees her ghostly image outside his bedroom window. At Sandra's house, the corpse of an elderly woman, Mrs. Holden, appears on her kitchen floor. Sandra calls Gerry for help, but the body disappears as soon as Gerry arrives. The two search the house but are disturbed by many occurrences, such as a window breaking, with the glass then dripping human blood.
Meanwhile, Bob has taken refuge in the garage of a local man, Mr. Ross. Ross's teenage daughter Ann finds Bob and offers him marijuana. Ross bursts in and attacks Bob, fearful he is trying to seduce his daughter. Ross kills Bob by impaling his head through a drilling lathe.
The following morning, Peter and Mary arrive at the graveyard that Mary saw in her vision. They begin searching for Father Thomas' tomb and meet Gerry and Sandra. They go back to Gerry's office to discuss Father Thomas' death when the four are showered with maggots. Gerry then receives a call from John-John explaining Emily has returned and killed his parents. They rush over to the Robbins' house and try to find the sheriff. While Sandra tries to get John-John to safety, Emily rips her scalp off. John-John runs through the town's streets and is saved by Gerry, who hands the boy over to the police.
While drinking at a bar, Mr. Ross is attacked by the re-animated dead people of the town, led by Bob. Ross and two other men are killed, as a state-of-emergency is declared over the radio. Mary, Peter, and Gerry arrive back at the graveyard as the clock strikes midnight and All Saints Day begins. They descend into Father Thomas' family tomb, discovering a cave of skeletal remains and cobwebbed putrescences. Appearing as a zombie, Sandra kills Peter before Gerry impales her with a metal spike. Mary and Gerry continue until they face Father Thomas, commanding an army of the undead. Before he can kill Mary, Gerry grabs a wooden cross and disembowels Father Thomas. The priest and the other revived corpses burst into flames and disappear. Mary and Gerry exit into the graveyard in the morning to see John-John and the police. Mary is relieved to see John-John alive but becomes frightened and screams as he runs towards her.
