Two women are murdered in the shrine town of Walsingham, north Norfolk, not far from Dr Ruth Galloway's home. It is a place famous for hosting visions of the Virgin Mary and full of superstition. DCI Nelson finds it a frustrating town in which to separate fact from religious myth. A friend of Ruth's who is a priest has been receiving threats. The letter writer knows far more about her than they should - and the letters suggest Ruth's friend will be next. There is an avenging angel on the loose in Walsingham. Ruth had better pray that she and Nelson find them before they strike again.