It is April in the Wicklow mountains and a young woman is found dead, seemingly sacrificed. Accompanying her body is Chapter One of The Rule Book - a self-help guide for serial killers. The case is assigned to the National Bureau of Criminal Investigation and headed by Detective Superintendent Colm McEvoy. Since the recent death of his wife, McEvoy is a shadow of his former self - two stones lighter with a wardrobe of ill-fitting suits, struggling to quite the cigarettes that killed his wife, and still getting used to being a single parent. Less than twenty-four hours later a second murder is committed. Self-claiming the title 'The Raven', the killer starts to taunt the police and the media. When the third body is discovered it is clear that The Raven intends to slaughter one victim each day until The Rule Book is published in full. With the pressure from his superiors, the press, and politicians rising, McEvoy goes after a killer that is seemingly several steps ahead. Is the Rule Book as definitive as The Raven claims?