In the spring of 1912, American writer Arthur Pearce is reeling from the wounds inflicted by a disastrous marriage. But his plans to travel abroad, write a new novel, and forget about his ex-wife are interrupted by a lovely young woman he encounters on a London-bound train. Her name is Sarah Coyle, and the tale she tells him chills his blood.

Sarah's younger sister has been entranced by Count Richard Dunning, who is rumored to dabble in bizarre religious rites and experimental medicine. Arthur agrees to help, but he has no idea of what awaits him at Altarbook, Sarah's ancestral mansion, or the remote English countryside, where Count Dunning and his followers are about to unleash an unholy supernatural power.