1826, St. Petersburg. After the suppression of speeches on Senate Square, the investigating commission begins to search for participants in the Decembrist uprising. Some of them come across to the authorities because of informers. Suddenly, a series of brutal murders take place in St. Petersburg: those who denounced the Decembrists become victims. Near the bodies of the dead, there is invariably a piece of paper with lines from a poem by the young poet Alexander Pushkin. A Moscow detective and a nobleman, Alexander Boshnyak, who was released from custody, take up the investigation of the case.