When Harpur and Iles are called in to investigate an undercover investigation gone wrong, they can sense dark, hazardous times ahead...

After a gang shooting involving an undercover police officer, Colin Harpur and his boss, Assistant Chief Constable Desmond Iles, are called to another Force's ground to investigate what the Home Office sees as spectacular failings. Harpur can imagine the pressure the officer would have been under. If a gang decided to kill, a spy would have to go along with it.

But with the careers of fellow officers ― who might be in secret, dangerous alliance with villains ― at risk, Harpur knows that he and Iles have an exceptionally tough inquiry ahead.