Detectives from the Third Gymnasium and the Secret of the Medallions

The rag seller Frosya and her son Keshka became accidental witnesses to a crime. A fleeing convict burst into the apartment of the Petersburg usurer Chvanov and demanded 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 ransacked the apartment and obtained that very medallion, which had become the reason for the murder. The boy hid the medallion, not even realizing that this trinket holds part of a secret cipher, and that exactly the same medallion with the second part of the cipher is now 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 was she whom the police arrested, accusing her of murdering the usurer.