In a prologue set in ancient Rome, the pagan Valerain attempts to abduct St. Cecilia to his debauched birthday feast, but her spiritual beauty stops him, and he kneels before her. In the main story, Conchita Cordova sings in the cathedral choir in her village of San Miguelito near the Rio Grande. Millionaire oil man John Rannie, whose oil fields have displaced the peasants, desires Conchita, and when he learns that her fiance, Juan Mendoza, has been employed by Adolf Wylie, a German spy, Rannie threatens to expose Juan unless Conchita gives herself to him. Although disillusioned, Conchita decides to save Juan, but as she removes her cross, Rannie is moved by her sacrifice, and begs forgiveness. Meanwhile, the villagers, incited by Wylie, set Rannie's fields on fire. When Juan, thinking that Conchita loved Rannie, throws her cross in the fireplace and places it on her breast as a brand of shame, she rebukes him. After Conchita saves Rannie from being burned by the villagers, he kneels beside her in church. In Rome, Valerain kneels before St. Cecilia.