Scene 1 - A small plaza in a poor neighbourhood of Madrid, at the end of the 19th Century. The brief Preludio culminates in the street cry of a flower seller which leads directly into the action. Two lovers, Cirila and Secundino, are enjoying some amorous banter under the eye of the local cobbler, Eulogio. He hears them make a date to dance that evening at the fiesta of Saint Isidro at the Pradera, the town meadow on the bank of the Manzanares river. When they leave, Eulogio gives the news to the bashful Pérez, who would like to accompany Cirila there himself.
Eulalio observes a fight brewing inside the nearby tavern between Señor Matías and Epifanio, an arrogant thug engaged to the old man's daughter Isidra, very clearly without any good will from the family (Dúo: "¡Toma, granuja!".) Epifanio eventually leaves with his friend El Rosca ('wheedler'), boasting that he will dance with Isidra next day at the Pradera, come what might. Isidra calms her father down, but Eulogio senses that the girl herself is tiring of her lover's belligerent behaviour. The cobbler feels that she would be better suited to the baker Venancio, a hard-working, steady man who secretly loves her deeply; and he determines to sound out her mother Ignatia on the matter.
Ignatia is quickly convinced of the benefits of his matchmaking plan, especially when Eulogio observes that her daughter is not badly disposed towards Venancio. The cobbler engineers a 'chance' meeting between Isadra and the baker, who plucks up courage to approach the girl. In a gentle Dúo: "Anda, y desembucha" he proves too shy to speak his mind directly, eventually deciding to buy a bunch of carnations to speak for him.
The course of true love is interrupted by Epifanio's return with El Rosca. The thug issues a threat to Venancio, warning him to steer clear of his property. The normally gentle baker is about to go for his throat when Isidra and Eulogio intervene; and Epifanio goes into the tavern, sneering at his fiancé as well as the baker. A crowd gathers, led by Isidra, ready to stroll down to the Pradera (Final: "Alegre es la mañana".) The girl refuses to confirm that she will dance with Epifanio, despite his hectoring, and Matías adds that she may dance with whomsoever she pleases. When Isidra announces that she would even prefer to dance with Venancio, the supremely self-assured Epifanio merely goes back into the tavern with a threatening laugh.
Scene 2 - The Toledo Bridge leading to the Pradera. Secundino is searching for Cirila in the crowd. She turns up with her baby sister in tow, much to his annoyance; but eventually they set off for the Fiesta, pursued by the jealous Pérez and his military friend Torrija.
Scene 3 - The fair on the Pradera. Barkers hawks their wares, and the crowd exuberantly enjoys the entertainments on offer (Coro: "Con tres ó cuatro orquestas".) Secundino has arrived with Cirila and the child, but thanks to some military distractions from Torrija Perez manages to disappear into the crowd with Cirila, leaving Secundino cursing his luck - and holding the baby!
Isadra arrives with her parents and their friends. They consider the various treats on offer, until to everyone's joy an organillo (barrel organ) starts up, and the dance begins. Epifanio turns up in truculent mood with El Rosca, but when he demands a dance Isidra turns him down point blank, nor will anyone else consent to dance with the overconfident braggart.
Venancio and Eulogio saunter in; and to Matías surprise, Isidra has no hesitation in agreeing to dance with the baker. It's now Venancio's turn to taunt Epifanio, who despite his threats is too cowardly to respond and becomes the butt of general humour. Goaded into a jealous frenzy the thug produces a razor, but he is quickly bested by Venancio and leaves crestfallen with his weasel-like friend. The sainete ends as all unite in praise of the happy young couple, who lead the interrupted dance with redoubled zest.