When her beloved husband Paul falls into a coma after a car accident, Commissioner Ellen Lucas ( Ulrike Kriener ) decides without further ado to leave her adopted home in Cologne and move to Regensburg. In the special clinic for coma patients there, she hopes for Paul's quick recovery.
In her professional life, she has no time to breathe deeply: in Regensburg the body of five-year-old Maria is found, who fell victim to a crime. The inhabitants of the idyllic small town are upset. Uncompromisingly and with sensitivity, Ellen Lucas goes to work to reconstruct the crime, often against the resistance of her new colleagues. The only thing she can rely on 100% in this extreme situation is Commissioner candidate Stefan Deuter ( Thure Riefenstein ). Contradictory statements by family members and dubious alibiversions also make it difficult to find the real perpetrator. Within the police apparatus, you are particularly concerned about the rivalry with your colleague Boris Noethen ( Michael Roll ), who sees the new as an intruder who could screw up his career advancement. When the supervisor Klaus Buddlick ( Arnulf Schuhmacher ) dies, the competitive relationship gains sharpness. Then comes another terrifying message: Little Ina is reported missing by her mother, and at the scene there is another blue flower that appears as a kind of business card for the perpetrator. The pressure on the investigators is growing, the fear that a serial perpetrator is at work can no longer be ruled out.

The residents of Regensburg are shocked. The body of 19-year-old Biljana Savic (Cordula Böck) is recovered from a branch of the Danube. The scars on the girl's body allow only one conclusion: murder. What particularly affects Commissioner Lucas (Ulrike Kriener) is the fact that the traces of abuse in the past as well as the present suggest. From Biljana's friend Milica (Miranda Leonhardt) she learns that both girls came to Regensburg two years ago through an au pair agency from Serbia. Young Milica looks frightened and refuses to comment further. Biljana's host parents, the Schwarz couple (Anneke Kim Sarnau and Felix Eitner), also remain silent.
What drives Milica into isolation and what is the couple hiding? In order to break the wall of silence, the commissioner turns to Father Danko, a priest from Croatia who knows how to relate the horrors of war in the recent past. The Croatian Tomislav Vodenac (Peter Davor), with whom Milica was being treated by a dentist, represents a completely different victim/perpetrator theory of the war. His relationship with Milica's host mother Isabell (Maria Bachmann) makes him suspicious. The situation escalates when inspector Lucas receives life-threatening threats and the unknown assailants do not shy away from attacking their landlord Max (Tilo Prückner).
Inspector Lucas can only understand how the crime is related to the recent European past when it is almost too late, because suddenly Milica has disappeared ...