Prosecutor Katja Schilling is leading a murder trial against the powerful underworld boss Mankoff. But more and more witnesses are withdrawing their incriminating statements in court, because Mankoff's arm still reaches far from prison. All the more important is Nadescha Schaposchnikow, the sister of the young murdered drug courier, who observed Mankoff's crime and is willing to testify as a key witness. Katja keeps them hidden in a secret place until she makes a statement. However, the committed public prosecutor is ambushed herself: an informant and former fellow student is murdered - with her pistol. Ironically, Chief Inspector Tom Schilling, her husband, with whom she is divorced, takes up the investigation and soon finds her trail. Katja is torn: Can she confide in her husband or is he the mole who keeps supplying Mankoff and his organization with secret police information? Her fatherly friend Mirko Nolte, also a detective and Katja's most important confidante, has her back as best he can. But then Nadescha suddenly disappears from her hiding place. Katja must do everything she can to save her witness' life.