Dutch composer Simeon ten Holt achieved worldwide renown in 1979, when his work for four pianos Canto Ostinato was first performed. Although some music experts viewed it with disdain - it broke with prevailing notions of serialism and tonality - the piece was a huge hit in the contemporary classical music world. In the years since, numerous musicians have released their recordings of Canto, and it is still being performed around the world. Director Ramon Gieling interviewed a large number of people about the sometimes far-reaching impact this composition has had on their lives. One interviewee tells of how Canto was the soundtrack to the birth of her son; another has a section of the score tattooed on his arm. Gieling seeks to unravel the mystery of the universal power of music, and his blend of documentary footage, fiction, essays and archive material produces a multifaceted response to the question of just what it is about this piece that touches people so deeply.