A knife attacker kills two people in Hanover under the cover of a dense crowd. The nationwide investigation team, including Chief Inspectors Thorsten Falke and Anaïs Schmitz, faces a difficult task: There is no trace of the perpetrator. And there is a danger that he will strike again. To gather possible clues, the decision is made to use the innovative software KROISOS. After a comprehensive data analysis, the program quickly presents a likely perpetrator: the mentally ill René Kowalski. His sister Nora, however, considers it impossible that her brother is the perpetrator. Falke also remains skeptical. Then another crime occurs, almost identical to the first, overturning all certainties...