Pioneer leader Serge, a sculptor, decides to work in a new plastic material, among creatively gifted children in a camp located in an old mansion. Pioneer Lopukhin is so in love with his classmate Ergolina that he does not notice how fascinated Sonya Zagremukhina is with him. Showing their emotions and moods helps their participation in the production of the play "Masquerade" by Lermontov, and the play itself imperceptibly turns into a drama with unexpected confessions, insults, jealousy, and outbursts.
