Detectives from the Third Gymnasium and the Secret of the Medallions

The rag dealer Froska and her son Keshka became accidental witnesses to a crime. A runaway convict burst into the apartment of the Petersburg usurer Chvanov and began demanding some medallion from him. The conflict quickly escalated into a scuffle, during which the usurer was killed. Taking advantage of the moment, the mother and son raided the apartment and obtained the very medallion that became the cause of the murder. The boy hid the medallion, not even realizing that this trinket holds part of a secret code, and that an identical medallion with the second part of the code is currently warming on the killer's chest. But before the mystery of these decorations is revealed, the boy will have to save his mother... After all, it is she who was arrested by the police, accused of murdering the usurer.