The story takes place in the former Soviet Union during the Stalin era. The protagonist Leo Demidov is an agent of the Soviet Ministry of State Security (MGB). He is loyal to his duties, loves his country, and is full of idealism. As a combat hero, Leo enjoys special treatment from the state. Not only does his family live in a luxury residential area in Moscow, but his parents are also allocated a good apartment. Although he was secretly arrested and tortured, Leo believes that this is all for the national interest. However, a series of child murders changed Leo's life trajectory. The government was unwilling to admit the facts of the murders. Leo, who was determined to catch the murderer, became the target of government suspicion. Only his wife always stood by his side...