Billy Nelson is back home in battle-scarred Belfast. But the Troubles have cut this ex-Army Loyalist hard man deep - and now that his city's allegiances have shifted, nothing is quite the same. An outbreak of gang violence forces Billy to move on. This time to Edinburgh, where he muscles in on the capital's drug trade and the family who run it. As the balance of power tips, underworld rivalries between Edinburgh, Glasgow and Belfast spill out onto the streets. With a spate of horrific incidents and a trail of victims, the pressure is mounting for Grace Macallan, new superintendent of the Crime & Counter Terrorism Directorate. Troubled by her own demons and with everyone baying for the blood of Billy Nelson and his old paramilitary contacts, can Grace hold her nerve?