A Song is a documentary etude on youth, made in the spirit of cinéma vérité. The film employs observational methods to examine popular leisure activities of the Czechoslovak youth in the 1960s, from going outdoors through various sporting activities to musical practices.

The employees of the furniture company MARS welcome a rare visitor with hired music. Their boast that they would put together an orchestra is taken seriously, so they receive a small gift - musical instruments for thirty musicians.