The Upper-class Violet and her fiance Teddy are spending Christmas in Violet's Yorkshire family home with their close friend Tom and his new girlfriend Maddie. But when toxic histories and an illicit affair means Christmas doesn't go her way, Violet breaks her family's cardinal rule... she puts the fire out. Without realizing, she lets in an ancient pagan beast that terrorizes her and her friends to complete a mysterious, deadly ritual - leaving Violet, and her secrets, with nowhere to hide.