On the shocking discovery of a passenger's body on the Great Western Railway excursion train, Detective Inspector Robert Colbeck and his assistant, Sergeant Victor Leeming, are dispatched to the scene. Faced with what initially appears to be a motiveless murder, Colbeck is intrigued by the murder weapon – a noose. When it emerges that the victim had worked as a public executioner, Colbeck realises that this must be intrinsically linked to the killer's choice of weapon. However, the further he delves into the case, the more mysterious it becomes. And when a second man is strangled by a noose on a train, Colbeck knows he must act quickly; can he catch the murderer before more lives are lost?