A chief commissioner investigates the murder of a young woman and a fatal car accident. Apparently there is a connection between the two cases.

Karen, a maths teacher, finds herself involved in a traffic accident for which she is not to blame. The accident causes the death of a girl on a scooter. Although innocent, the young woman is distraught, more so when she discovers that the dead girl – Miriam – is none other than the sister of her pupil, Lukas. The more everyone around her assures her that she is not to blame for the girl’s death, the guiltier Karen feels. To her, the accident is like an equation that just doesn’t add up. In an attempt to make up for her actions at least in part, she begins to give Lukas extra maths lessons. But, consumed by his pain, the boy wants much more from her.

Chief Inspector Johannes Fischer has retired in the meantime. The last case he investigated together with his former boss Konstanze Satorius has been closed, but Fischer is still convinced that an innocent woman is in custody.

In a hospital in Hamburg, an unidentified woman is disconnected from the life-support system. While the investigators search for the mysterious perpetrator, two more men are murdered.

When Eva wakes up, her baby is calm. Too calm. Your child is no longer breathing. Desperate, she massages the little heart. For free. While still in shock, Eva makes a monstrous decision.

In a project with the concept of open-prison, Benjamin is given the unique chance of a new beginning. As one of seven juvenile offenders he should adopt social skills and experience security in a family-like community. But when he meets his house-mother Eva, he is shocked. She was one of his victims, but cannot recognize him because he was hidden by a mask. His brutal assault on her was never resolved. Ben does his best not to attract attention. But Eva's suspicion is aroused.