The rules aren't written down. You can't find them anywhere, but everyone knows what they are. They're the series of unwritten norms, what you can and can't do, and sticking to them is how the game's played. One prime example is that you don't kill police officers. Even hardened criminal gangs like the Krays and the Richardsons knew this and adhered to it. But what happens to those same rules when national security is invoked? Investigating what appears to be the arbitrary killing of a young police officer, DS Robert McGraw finds himself operating in a world where players have their own rules and the accepted rules have no meaning.