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.