Anton Ivanovich Voronov is a highly respected professor at the Moscow Conservatoire, who places the music of Bach above everything else and regards it as the ultimate yardstick by which other musical accomplishments must be measured. His daughter, Serafima, is an aspiring singer with great potential, and her father’s anger is aroused when she begins singing in the operetta composed by Aleksei Mukhin, thus abandoning what he considers the higher calling of opera. Mukhin’s work, however, demands a high level of ability from his soloist, and Anton Ivanovich is persuaded of the legitimacy of operetta as a musical genre when, in a dream, he is visited by Johann Sebastian Bach himself, who tells him that ‘people need all kinds of music’.