Scene 1 - the market square of Zaragoza in Aragon. A short Introducción giving a taste of many of the folk elements of the zarzuela precedes the opening scene. Antonia, Juana and the other market women and customers are arguing heatedly over prices, until the popular butcher Isidro appears and calms everybody down (Coro: "Hay que separarlas"). Timoteo, a timorous officer of the local guardia, posts up a decree announcing that the Municipal Council are going to double local taxes. He has the tricky task of trying to balance his official duties against local loyalty, particularly as he is the husband of the fiery Antonia (Salida: "El Ayutamiento".) Not surprisingly he is attacked by the women in the combative Jota: "Anda, vé y dile Alcalde." Pilar, Isidro's adopted niece and assistant, argues most fiercely on his behalf. Several men have fallen for the passionate girl, but she has remained staunch to her beloved Jesús, a conscript fighting with the army in Cuba. One soldier in particular, an Andalusian Sergeant, is determined to capture her by force, or by stealth.
Pilar only lives to receive a letter from Jesús. Finally the postman delivers it, and in her touching Romanza: "Esta es su carta", she despairingly regrets the fact that as she cannot read, she must rely on other people to give her his news. Is he surviving the heat and dangers of Cuba? Does he still love her? Will he ever return? Antonia tries to help her, but can't make out the meaning either, and in the end Pilar has to ask Pascual, a young man known to all as "Jeremiah" - owing to his melancholy sighing for Pilar - to read the letter to her. Jesús is well, but the war is going badly, and he hopes to be sent home soon. The Sergeant tells her that he has had a more recent letter, telling him that Jesús has married a Cuban woman, and advising Pilar to seek the protection of his "best friend" the Sergeant himself. Pilar is unsettled - though she doesn't really believe the man, and finally taunts him, saying she would rather wait for Jesús to become a widower. The market women meanwhile have decided that enough is enough, and Pilar leads them in revolt against the new taxes in another powerful Jota: "Si las mujeres mandasen". The scene ends in colorful riot as Timoteo, frightened by his wife's threats of marital disharmony, breaks his sword and leaves the guardia.
Scene 2 - by the river Ebro, on the fiesta day of the Pilarica, Zaragoza's basilica-cathedral. Poor Timoteo has gone fishing to try and catch something to eat. The first repatriated troops land from Cuba, more dead than alive (Coro de repatriados: "Por fin te miro, Ebro famoso".) Jesús is amongst them. He cannot wait to greet his mother, and his beloved Pilar, once again (Solo: "Por la patria te dejé, ay di mí".)
Scene 3 - the main square, in front of the Cathedral. In the Coro: "Por ver a la Pilarica" a group of bumpkins from the local farms joyfully anticipate the traditional parade of elaborately dressed stilt-walkers - gigantes - and huge, carnival dwarf-heads - cabezudos. Soon the huge and gaudy monsters appear in the Salida de los gigantes y cabezudos, with its colourful, rustic instrumentation. Pilar, come to celebrate her nameday festival as best she can, leads the praise of the Aragonese carnival in another tremendous Jota: "Luchando tercos y rudos".
The Sergeant pursues his stratagem, telling Jesús that Pilar, tired of waiting, has married a rich American. In despair the boy decides to collect his kit from the barracks and leaving the city for good. Sure she has heard Jesús' voice in the throng, Pilar plays a trick on the Sergeant. Producing an old letter, she asks the Andalucian to read it to her. He tells her that Jesús has been killed in an enemy ambush and died begging Pilar to marry "my good friend, the Sergeant", so revealing his plot as a pack of lies. Ashamed, he confesses the truth and Pilar, sorry for his pathetic machinations, forgives him. The Sergeant in his turn goes to find Jesús at the barracks and tell him to meet his beloved at the door of the basilica. Things are looking up: even Timoteo is to get his old job back.
The Carnival figures return, and the zarzuela ends combining the song of the returning soldiers with a grand musical Final apotheósico: "Salve a la Virgen del Pilar" in praise of the Virgin of the basilica - and by extension of the staunchly faithful girl who shares its name. At last Jesús runs to meet his Pilar, and the lovers are reunited.