In a small New England town called Dunwich, a priest commits suicide in the cemetery, hanging himself from a tree. This act of desecration opens the gates of hell, threatening to unleash the dead upon the world. The local residents are unaware of the dark forces at work, but strange and terrifying events begin to unfold. A psychic in a nearby city, Mary Woodhouse, experiences a horrific vision during a séance, which results in her apparent death and burial. Reporter Peter Bell investigates the story and discovers unsettling occurrences connected to the priest's suicide.

Mary, who has been buried alive, is rescued by Peter, and together they team up with a local psychiatrist, Gerry, to investigate the ominous events plaguing Dunwich. They learn of an ancient prophecy that if the gates of hell are not closed before All Saints Day, the dead will rise to consume the living. As they seek to understand the connection between the priest's death and the apocalyptic forewarning, bizarre phenomena escalate. Townspeople are subjected to gruesome deaths and supernatural visions, suggesting that the end is near unless the trio can somehow reverse the curse and close the gates of hell.