Pioneer leader Serge, sculptor, decides to work with new plastic material, creatively gifted children, resting in the 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 by 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, outbursts. The teens are so busy with their feelings that they do not pay attention to the pedagogical ideas of Pioneer Serge, and by the end of the film they without any special encouragement are ready to become a commemoration of first love.