When a Catholic priest is murdered in a foggy London street, the only clue is a list of names found hidden on his body. Mark Easterbrook, a historian with an analytical bent, becomes drawn into the mystery after one of the names on that list belongs to a young woman whose recent death he had no reason to question. His curiosity hardens into suspicion when he hears whispers of a converted country inn called The Pale Horse, where three women with reputations as witches are said to arrange deaths to order. The rumour is absurd on its face: that a person can be killed at a distance through ritual and suggestion, with no poison, no weapon, and no trace, the victims appearing to succumb to ordinary illness. Refusing to accept either the supernatural explanation or the convenient coincidence of so many natural deaths, Mark sets out to test the operation from the inside, recruiting allies who are willing to take real risks to expose how the deaths are actually engineered. The investigation moves between a sleepy village, antiquarian London, and the patient routine of police work, with the detective novelist Ariadne Oliver lending her sharp, scattered insight. As Mark closes in, the danger turns personal, and the line between coincidence, fraud, and something stranger grows harder to hold. The result is a puzzle built around a method of murder so quiet that no one thinks to look for a murderer at all.