DCI Steve Burt and his team have been asked to determine whether a serving RAF officer is a spy. If he is, then a kill order on him, issued by a clandestine MI5 department will be enforced. As Steve and his team are grappling with MI5 and their demands, they are given a double murder case that has all the hallmarks of a professional hitman. A very determined killer is seeking revenge on the four men responsible for his eight years in prison and the murder of his wife and young son. The killer has put the knowledge he has acquired in prison into practice, meaning the team have no clues, no forensics and no witnesses. This proves to be a difficult and frustrating case and DCI Burt has to use all his experience to track down this elusive killer