When the body of a woman in a blue dressing-gown is found dead, it is clear that a horrible crime has been committed and DCI Nelson and his team are called in. Ruth, a devout atheist, is amazed to discover that her old university friend, Hilary Smithson, is now a priest. Hilary has been receiving a series of vitriolic anonymous letters targeting female priests. When another female priest is targeted and murdered, the race is on to unmask the killer before they strike again.