Roman Kurykin, an amateur jazzman and the owner of an absolute ear for music, cannot reconcile himself to the idea that his son Edik does not show any interest in music. The dejected father, in desperation, suspected that the child could have been replaced in the maternity hospital by mistake. He got the addresses of two families where the sons were born at the same time as the younger Kurykin. Kurykin reports his suspicions to two other fathers, Shulgin and Sazonov. In secret from their wives, husbands begin their investigation.