Canción del alma tells the tale of José Luis Barrera, a Federal colonel, who reluctantly must leave behind his sweetheart, Esperanza, when he is called to battle. After a romantic parting kiss interrupted by his arch-enemy, Salgado, Esperanza follows him to the battlefield so that they can be married before he dies in battle. José Luis is shot right in front of her and he dramatically falls into a nearby river. Esperanza quickly lights the gunpowder laid to destroy the enemy defences, and is thus taken hostage by Salgado and his men. As revenge, she locks Salgado in a barn after his attempts at seduction, and he accidentally drops a cigarette, causing the barn to set alight and he dies. She manages to escape and the film flashes forward through her pregnancy with José Luis's child, which she brings up at the home of a kind gentleman, Pancho, who takes her in after she faints in his doorway.