Yaroslavl 1975. Two high-profile crimes in one day. A mentally ill physicist cuts off his neighbor's head and brings it to the police, and a body is found in the basement of an apartment building a criminal killed by an awl in the ear. An uncompromising investigator for especially important cases of the prosecutor's office, Egor Tabolin, enters into a duel with an elusive killer, to whom the threads of both cases lead. His enemy is cunning, treacherous and omnipotent. With the help of blackmail, he managed to subjugate the most influential people in the city. The KGB is behind him. But investigator Tabolin will not step aside. He seeks the "ultimate measure" of justice for the victims, and the "ultimate measure" of punishment for the violent criminal.