KGB lieutenant colonel Mikhail Shirokov is informed that his long-time enemy Aleksandr Stroganov, nicknamed Graf, a former punisher and saboteur who worked for German intelligence during the war, has been spotted in Leningrad. With the help of the remnants of the White Guard underground, the sabotage group "Zigzag" and "mole" in the ranks of the police, he had to carry out a sophisticated plan to destroy the city. The task is the explosion of five symbols of the revolution, the main goal of which was the Big House. Young Mikhail Shirokov, then an operative officer of the NKVD and his teacher, senior lieutenant Eremeev, prevent this catastrophe, all the conspirators are destroyed, but Graf Stroganov manages to escape. In 1965, Lieutenant Colonel Shirokov checked all the Stroganovs now living in Leningrad. Suspicion falls on projectionist Stroganov. Indeed, he and his wife Lora were abandoned in the USSR by American intelligence. Their goal is to kidnap a prominent nuclear physicist and take him abroad. Shirokov and his group follow the trail.
