While tending to his garden, William Jones uncovers an unusual stone head. That night, his wife is plagued by terrifying nightmares, prompting William to remove the head from their home. He brings it to an archaeologist at Bangor University, who specializes in Celtic artifacts and is excavating other Celtic remains. However, when he accompanies her back to her home for further analysis, strange and sinister events begin to unfold at night, unleashing a grotesque half-human, half-animal entity. As the archaeologist's family members fall victim to the creature, they face terrifying deaths and become sacrifices to the ancient Celtic gods.