As Sister Ann (Debbie Reynolds) embarks on her mission from the peaceful surroundings of her Dominican convent near Antwerp to Samaritan House located in one of Brussels' most impoverished neighborhoods, she carries with her a profound passion for music. Her guitar and enchanting voice quickly transform into the heart of evening singalongs at the shelter, allowing her to win over not only the camaraderie of her fellow nuns but also the affections of Father Clementi (Ricardo Montalbán) with her harmonious melodies.
During this time of belonging and connection, Sister Ann forms a unique relationship with Dominic Arlien (Ricky Cordell), a young boy yearning for direction in a world where maternal love seems absent. His only comfort is his 17-year-old sister, Nicole (Katharine Ross). Moved by the challenges Dominic faces, Sister Ann crafts the heartfelt song "Dominique," which strikes a chord with all who listen.
Father Clementi soon notices Sister Ann's remarkable gift and encourages music executive Robert Gerarde (Chad Everett) to hear her beautiful compositions. When Robert meets Sister Ann, he experiences an overwhelming sense of déjà vu, recalling their days as classmates at the illustrious Paris Conservatory of Music five years earlier. However, a visit to the Arlien home unveils unsettling truths - Sister Ann finds revealing photographs of Nicole, taken out of desperation to provide for her family. The reaction from their father, compounded with anger upon learning of their hidden truth, escalates into violence, resulting in an eviction for both Nicole and Sister Ann. Subsequently, the Mother Prioress (Greer Garson) admonishes Sister Ann for letting a painful family secret out into the open.
As "Dominique" rises to international acclaim, Robert's growing affection for Sister Ann becomes evident. He secures permission from church officials to produce an album with her, and the song captures the heart of the world. Captivated by Sister Ann's extraordinary talent, Ed Sullivan makes his way to Brussels with a television crew eager to showcase her giftedness, even offering a jeep as part of the deal for their African mission.
Navigating the dizzying reality of her sudden fame alongside Robert's romantic advances, Sister Ann turns to Father Clementi for counsel. However, her world is shattered when Dominic is involved in a serious accident. In a moment of desperation, she makes a solemn vow: if he survives, she will forsake her music for a life dedicated to helping others. Miraculously, when Dominic recovers, the Arlien family acknowledges the need to rethink their priorities, ultimately deciding to move to the countryside.
In an act of generosity, Sister Ann gifts Nicole her guitar before embarking on a path of self-exploration, driving through various African villages in a jeep adorned with "Dominique" written across its back, a symbol of hope and transformation.
