Billy Nelson is back home in Belfast, but the Troubles have cut this ex-Army Loyalist hard man deep and his city's allegiances have shifted. An outbreak of gang violence forces him to Edinburgh, where he muscles in on the drug trade. Underworld rivalries between Edinburgh, Glasgow, and Belfast spill onto the streets. The pressure mounts 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, can Grace hold her nerve?