Stockholm is rocked by an explosion on an underground train. When A Unit begins investigating, they uncover a fascist gang with ties to far-right groups all across Europe and its leader becomes their prime suspect. Kerstin is struggling to come to terms with the death of Bengt and her working relationship with Paul suffers as a result.

In their search for the bombers of an underground train, 'A' Unit has uncovered a fascist gang with links to terrorists across Europe. But as their net tightens around the suspects, another survivor emerges from a hiding place in the tunnel with information that will take the investigation in surprising new directions.