1826, St. Petersburg. After the suppression of speeches on the Senate Square, the investigative commission begins searching for the Decembrists. Some of them are caught by the authorities because of informers. Suddenly, a series of brutal murders takes place in St. Petersburg: the victims are those who denounced the Decembrists. A piece of paper with lines from a poem by the young poet Alexander Pushkin invariably remains near the bodies of the dead. A Moscow detective and a nobleman released from arrest, Alexander Boshnyak, are taking over the investigation of the case.