Big House.

Leningrad, 1965. KGB Lieutenant Colonel Mikhail Shirokov is informed that his long—time enemy Alexander 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 Zigzag sabotage group and the mole in the ranks of the militia, he tried to carry out a sophisticated plan to destroy the city: the explosion of five symbols of the revolution, including a Large House. The young Mikhail Shirokov, then an NKVD operative, and his teacher, senior Lieutenant Yeremeyev, prevented this catastrophe, but the Count managed to escape. Shirokov checks all the Stroganovs currently living in Leningrad, suspicion falls on the projectionist. Indeed, he and his wife, Laura, were abandoned in the USSR by American intelligence. Their goal is to kidnap a major nuclear physicist and take him abroad. Shirokov and his task force are on the trail.