When a headless body is discovered on a popular jogging trail, Detective Inspector Bernard Watts and his team are plunged headlong into a baffling murder investigation. Why would someone stab to death a young woman on her daily run - and take her head? When a close examination of the crime scene results in a shocking discovery linking the present murder to a past crime, criminologist Will Traynor is brought in to assist the police. Aware of Traynor's troubled past and already having to deal with inexperienced rookie PC Chloe Judd on his team, Watts is sceptical that Traynor will bring anything useful to the investigation. He's about to be proved very wrong ..