Mrs Bradley is not unaccustomed to receiving fan mail, but the anonymous letter that she opens one morning at breakfast has not been sent by a well-wisher. The letter evokes memories for Mrs Bradley of a past criminal investigation, in which she had played a minor role in convicting a particularly unpleasant murderer and satanist. The letter, too, provokes a link to a sudden spate of gruesome and ritualistic murders occurring in the normally tranquil surroundings of the Norfolk Broads and, not for the first time, Mrs Bradley finds herself drawn into a race to track down a killer.