The Düsseldorf Art Academy is the scene of a mysterious murder. While working in the plaster workshop, student Till Bornemann is strangled by a masked man. Till's girlfriend, Pia, who was posing for a plaster cast, didn't see anything, but she heard the unsuspecting Till address his killer as "Gereon." However, art student Gereon Müller claims to have nothing to do with the murder, leading Inspector Flemming to suggest that the perpetrator might have used one of the masks he himself made.

Flemming and his team are dealing with the murder of a woman believed to be mentally ill and irregularities in a clinic.