A car-bomb attack in a quiet suburban street brings back unwelcome memories for Jack, when evidence points to the involvement of a Northern Irish terror group, long thought inactive. As the family of the victim seek their own form of justice, Jack calls an old friend to help them find those responsible and stop the act of revenge from escalating.

Nikki is humiliated in court when a barrister accuses her of making a serious error in the case of a policeman who may or may not have been murdered.

Meanwhile the team investigates the death of a medical researcher found in a canal with mysterious puncture marks on his body.