April 1958. Maria Krapivina, a graduate of the law faculty of Leningrad University, Department of criminal procedure and criminalistics, is assigned to the UGRO of the Central district police Department. Just a girl, an excellent student, the daughter of intelligent parents falls into a team consisting of rough and experienced operatives who have passed the war. On the first day, Masha wants to quit. But she gets her hands on information about a traitor in the Department associated with a large and audacious gang. Masha decides that it is her duty to stay and uncover the "mole". And also to prove that it is worth something. Everyone falls under suspicion, including the head of the Opera Department of the Swedes ,the "uncouth lout", with whom Masha unexpectedly falls in love, and every day more and more.