Deep in the isolated and decadent hill country of Dunwich, Massachusetts, a strange and deformed woman named Lavinia Whateley gives birth to a preternaturally fast-growing son named Wilbur. Raised by his grandfather, a man whispered to practice black magic, Wilbur develops into a monstrously erudite scholar with an unnatural appearance and an aura of dread. The household is plagued by mysterious noises from the hills, an ever-present and nauseating stench, and the unexplained disappearance of livestock. Following the deaths of his grandfather and mother, Wilbur travels to Miskatonic University in Arkham to consult the forbidden pages of the Necronomicon, seeking a specific incantation involving the cosmic entity Yog-Sothoth.
His violent end at the university library exposes only the horrific prelude to a greater nightmare. Left behind in the abandoned Whateley farmhouse is an invisible, rapidly growing entity—Wilbur's twin brother—born of a monstrous non-human lineage. Nourished by sacrifices, this gargantuan abomination breaks free and begins a path of destruction across the terrified countryside, crushing buildings and slaughtering livestock with titanic force. The local populace is paralyzed by superstitious fear, leaving the defense of the region to a small group of academics from Arkham.
Dr. Henry Armitage, alongside Professor Rice and Dr. Morgan, decodes Wilbur's dark diary and realizes the full extent of the threat. They discover that the creature is attempting to open the dimensional gates for the ancient, formless Old Ones, who seek to reclaim the earth and erase humanity. Racing against time and terror, the three scholars ascend Sentinel Hill to confront the invisible horror. Armed with an experimental chemical powder to reveal the entity and a potent ritual incantation, they execute a desperate plan to banish the monstrosity back to the cosmic abyss from which it was summoned.
