Berti and Marchetti investigate the murder of Sarah, an irreproachable thirty-year-old secretary of an important financial broker. Her mother Daniela, worried about the girl's silence, finds her body, hermetically sealed in the closet of her house. Commissioner Fontana takes care of the difficult case (the murderer seems to have left no trace), also committing himself to mending the relationship with Nina: in fact, the girl has decided that she no longer wants to collaborate and is leaving with Major Patrizi for a secret location in Germany.