The rebus found on a note at the bottom of Rosa Bastiani's throat, a mother of a few months old baby stabbed in a park, kicks off complex and painful investigations, which will put Rocca and his colleagues to the test. Everything will become more difficult when one of the sisters of Carabiniere Banti will be involved. The marshal, putting his life at risk, will investigate Professor Aleppi, headmaster of the school, discovering a past made up of injustices, traumas and suffering. Once the case is resolved, Rocca and Margherita obtain custody of Bastiani's orphan.