Fanciful biography of the Belgian nun who briefly made the hit parade.

Sister Ann leaves the Dominican convent near Antwerp for her assignment at Samaritan House in a depressed area of Brussels. Sister Ann loves to play the guitar and sing, and when she joins in the traditional evensong at Samaritan House, she impresses the other nuns and Father Clementi. She becomes fond of Dominic Arlien, a motherless child whose father is an unemployed drunkard and who is loved only by his 17-year-old sister, Nicole. Sister Ann composes the song Dominique for the boy. Father Clementi persuades Robert Gerarde, a partner in a recording firm, to listen to Sister Ann's music in the hope of having it recorded. When Robert meets Sister Ann, he discovers that she was his classmate at the Paris Conservatory of Music 5 years ago. Later, while visiting the Arlien house, Sister Ann discovers pictures of Nicole in provocative poses; the girl defiantly tells the nun that she posed to get food and rent money for her family. Her father overhears them, strikes Nicole, and orders the nun out of the house. The Mother Prioress later admonishes Sister Ann for allowing the young girl's secret to be made known to the father. Robert, whose attraction to Sister Ann has been rekindled, obtains permission from church authorities to have her record an album; Dominique becomes a worldwide hit, and Ed Sullivan brings a television crew to Brussels to film Sister Ann for his show. Sister Ann becomes confused by her success and by Robert's personal interest in her, and she seeks counsel from Father Clementi. Her decision is made for her when Dominic is seriously injured in an accident; she prays for him, promising to give up her music and care for others if he recovers. The boy recovers, and the Arlien family, shaken by the incident, decide to move to the country. Sister Ann gives Nicole her guitar and goes to an African village to work among the natives.