There are five musical numbers, none of which has much to do with the action - indeed, only one of the main characters, the likeable Matías, has anything to sing at all. Nonetheless, the farcical 'choir practice' and the catching Canción Húngara, with its strong gypsy rhythms, are memorable enough have ensured Alma de Dios a consistent place in the repertory. Its gritty realism and tentative conclusion suggest that Álvarez rather than the sunnier Arniches may have provided the guiding hand for the libretto.
Scene 1 - A run-down tenement in the poor quarter of Madrid. Timid Signor Matías has been left in charge of domestic duties by his "dragon" of a wife, Ezequiela. As he desperately tries to rock the baby to sleep whilst simultaneously keeping the stove burning with the aid of an inadequate little bellows, his friend Saturiano comes in. Having lost his job, he offers to help Matías with the chores on condition that there's a free meal at the end of it. They soon get bored with domestic duties, and pass the time of day by chatting up a pretty young neighbour through the window. Before things can get interesting, Ezequiela appears, delighted to be able to scold them out for their hopeless idleness.
When supper appears, so does Eloísa, fiancée of Ezequiela's nephew Agustín, looking pale as death. The young couple's happiness is threatened by rumours that Eloísa has secretly had a baby. The facts are very different. Eloisa, left an orphan when very young, had been brought up in her uncle's house with her cousin Irene. Irene took a lover, and when the worst happened the two girls agreed to pretend that Eloisa was the mother - for the very sensible reason that Irene was about to marry a wealthy old man, Signor Adrián. Agustin threatens to break off the engagement unless Eloísa proves her innocence. Surely, all she needs to do is point to the baptismal record at the church of San Lorenzo to reveal the true mother. Eloísa is loathe to bring shame on the good people who brought her up, but when Ezequiela learns that the suspicious Adrián is also on the case, she takes matters into her own hands and marches Matías off to San Lorenzo to establish Eloísa's innocence.
Scene 2 - The Vestry, San Lorenzo. After an Intermedio, the choirmaster, Don Ramon, is attempting to take a practice, with farcical results. His treble, Carrascosita, has a breaking voice - and when Ramon calls for the organ and a barrel-organ starts up instead, he gives up and calls the whole thing off until the morning, much to Carrascosita's delight (Rehearsal of the Mass: "Gracias agimus tibi".) Choir and organist depart, leaving the Sacristan, Signor Orencio to write out a wedding certificate in peace. Señor Adrián comes in with his friend Pelegrin, Irene and her mother Marcelina. The nervous Irene makes an excuse to leave with her mother, just before Ezequiela hurries in with Matías, Eloísa and Agustín. When Orencio eventually gets round to producing the baptismal record, he announces to general surprise that the mother is Eloísa after all. Adrián leaves triumphantly with Pelegrin, and Agustín throws over Eloísa in disgust. Ezequiela is the only one who still believes in the girl's innocence, and the scene ends with her marching Mathías off again in tireless pursuit of the evidence.
Scene 3. The Street, that night. Matías, bellows in hand, is selling roast chestnuts, hoping to overhear some clue as to the whereabouts of the baby. He flirts with a young chulapa, Balbina, singing her a dubious but jolly song about the uses of his little bellows. (Seguidillas of the Bellows: "Hoy me han dicho dos niñas".) Adrián is still not completely convinced his wife is innocent - certainly, Irene is still behaving strangely, and Matías overhears her in tearful conversation with her mother about the need to keep up the lie. Ezequiela gets Matias to follow them, and - finding out from the ingenuous Balbina about his flirtatious behaviour - ends the scene in pursuit of him once again.
Scene 4. A gypsy camp in the city. One of the women, Maria Carmen, sings a lively farruca, and the other gypsies, led by Tío Zuro and Pepe el Liso, improvise a lively dance. (Scene and dance: "la Farruca".) A troop of Hungarian beggars and vagabonds also makes an appearance, and one of their number leads them in the famous "Song of Hungary" (Canción Hungaro: "Canta mendigo errante",) a mixture of homesick nostalgia and praise of beggarly freedom. Matias, and Ezquierda with Agustin and Eloísa, finally arrive. Hiding, they catch Irene and her mother visiting the child, which is being cared for by another gypsy, Seña Rosa La Quema. Further deception is pointless, and Irene asks Eloísa's pardon, who swiftly forgives her. Agustin is relieved, and the lovers are happy again. The same cannot be said for Adrian. Coming in to see the child in his wife's arms, he bitterly denounces Irene, accusing her of the mockery of marrying an old man for his money. Cursing his fortune, he leaves, whilst the rest of them - even Matías - plead with Ezequiela to talk some sense into him. She good-heartedly agrees, and the sainete ends with "the dragon" charging off on another errand of mercy - this time without her Matías, relieved to be left to his own devices at last, dancing as the curtain falls to the strains of his little seguidillas.