Early 1930s Moscow. In an apartment, an important Party figure is found dead. The investigation is assigned to an experienced detective, Viktor Pavlovich Strel’nikov, who worked even before the Revolution, and his partner, young police officer Dmitry Belkin. The motives for the murder are unclear: the victim had no enemies, and there were no valuables in the house. An unusual cartridge found at the crime scene puzzled the investigators, because such ammunition and corresponding weapons do not exist in the records of the OGPU. Soon another murder occurs: this time the victim is an inebriated man from Khitrovka—again with the same unknown pistol. What connects these different people? With his vast experience, Strel’nikov suspects that the criminal must have a serious reason to eliminate both the Party man and the fallen alcoholic.