For the first time in his life, DI Tom Mariner's home life is beginning to look settled. There's talk of a move to the country and even kids, and while Anna is doing the talking, for once Mariner isn’t trying to evade commitment. The couple’s quiet holiday season is shattered, though, when an explosion rocks the day of a community carol concert. Tom and Anna are caught up in the aftermath of the event, and it remains unclear if the tragedy is accidental or an act of terrorism. Meanwhile, an unexpected reunion with an old friend thrusts Mariner into the unofficial investigation of a violent double murder to which he is inextricably linked. Mariner finds himself amidst a world of corruption where the boundaries between friend and foe are blurred.