Act 1, Scene 1 - The outer courtyard of a rich country house in La Mancha, during the 1860's at the time of the autumn sowing. Servants, shepherds and farm-hands are enjoying a celebration in honour of the Saint's Day of their young mistress, Sagrario, washing the homely feast down with zurra - white wine with water and lemon juice - and dancing a seguidillas. The revels are led by Catalina, a pretty serving maid (Coro y solo: "Aunque soy de la Mancha".)
The well-to-do peasant Carracuca is anxiously seeking Custodia, the elderly village wise woman. He begs her to save his wife Gertrudis, who has been suffering from hysteric fits which even Moniquito, the young caretaker from the local Hermitage of San Roque, has been unable to cure. Moniquito tries to use his position of authority to win Catalina's favours, but she rejects him scornfully. Don Generoso, a previous owner of the estate, appears. The old man lost all his money supporting the Carlist cause in the early years of the century, although he still lives on the estate. His misfortunes have turned his brain, and when he attempts to drill a group of cheeky village boys under the impression that they are a new "Carlist Army" come to liberate La Mancha, Sagrario has to defend the poor old man from the mockery of the crowd.
A group of farm-hands appears looking forward to the next day's sowing, amongst them Juan Pedro, a young man attached to Catalina. His memorably powerful celebration of the joys of the sower enthuses his audience (Canción del sembrador: "Cuando siembro voy cantando".) Moved by the song, Catalina asks her mistress whether Juan Pedro may speak up to ask permission to marry, and Sagrario agrees to receive the lad - on condition that Juan Pedro leaves the house afterwards, as it would not be proper for for an affianced couple to spend the night under the same roof.
When the farm-hand approaches, Sagrario lets him know her decision, though it is obvious that she is attracted to him herself. A proud woman, she has never known love, and asks Juan Pedro to explain this strange feeling to her. With increasing ardour he gives her a lesson in the language of love (Dúo: "Ama, lo que usté me pide"), but tactfully fails to pick up on her interest when he repeats some key phrases back to her ("Manchega, flor y gala de la llanura".) Juan Pedro dutifully asks Catalina to marry him, but the girl has heard the conversation between him and her mistress, and jealously refuses him.
Moniquito and Custodia talk to Don Generoso, who reveals the reason for his distraction - the disappearance of a son he once had by a local girl. Juan Pedro reappears. Despite Catalina's refusal, Sagrario still insists that the young man must leave the house next day, and his friends commiserate with his bad luck.
Scene 2 - Later that evening, in the village next to the house. Juan Pedro and some shepherds serenade their sweethearts. Everyone believes the farm-hand will address Catalina, but the verses he sings are aimed squarely at the mistress of the house (Nocturno-ronda: "Como soy nena mía".) The lascivious Moniquito meanwhile serenades one of the local girls, Carmelo, with a surprisingly risqué multiplication lesson in the dark shadows underneath a staircase (Pasacalle de las escaleras: "Dos por dos son cuatro".)
Scene 3 - Next morning, back in the courtyard. Catalina and the women of the house are peeling the saffron husks, supervised by their mistress. Sagrario sings of the delicacy of the saffron, whilst Catalina and the girls indulge in lively love chatter (Scena: "De mondar mucha rosa ... La rosa del azafrán es como la maravilla".)
Sagrario confesses her feelings to the wise Custodia, who tells her that Juan Pedro was a foundling, brought up in the local hospice. A relationship between them is clearly impossible; and drawing herself up in her pride, Sagrario calls the women back to work. As they begin peeling the husks once more, Juan Pedro and some of the men join in the work (Final: "Si quieres que te lo diga".) Working close to Sagrario, he makes his own feelings plain, but she proudly gives him the brush-off in no uncertain terms, and the people recognise the impossibility of any contact between them. Eventually Juan Pedro breaks away, and renouncing love as being fragile as the flower of the saffron, rushes away from the house for good.
Act 2, scene 1 - The village square, the following August. Ten months have passed. Catalina tells Custodia that in the light of Juan Pedro's continued absence, she has decided to settle for Moniquito. Carracura's wife has died of her "hysteria", and Juan Pedro surprisingly turns up to pay his respects. He leaves with Custodia, as Moniquito appears to ask formally for Catalina's hand. Rattled by her former love's reappearance, the girl decides that she can't take on such a dreadful prospect as the caretaker, and their love scene turns into a mutual slanging match (Dúo cómico y seguidillas: "Pero ven acá. No me vengas con lisonjas".)
A group of men offer condolences to the bereft Carracuca, who bewails the likely fate of his motherless children. The village women sing the praises of four alternative wives to solve the widower's dilemma, though Moniquito remains sceptical of the women's virtues (Tanguillo: "¡Conformidá! ... ¡Qué voy a hacer!".)
Juan Pedro runs into Sagrario. Convinced that he has really come back for Catalina, the mistress tries to leave; but when Juan Pedro declares his secret passion for her, she is honest enough to admit that she wants him too, proudly informing him that the difference in social status makes marriage impossible. He leaves heartbroken. Alone, Sagrario expresses her complex feelings in the subtle, melancholy Romanza: "No me duele que se vaya".
Juan Pedro asks Custodia whether anything can be done. She proposes to solve his problem -and Generoso's madness - by passing him off as the old man's lost son, and after some internal debate he agrees to the ruse. Catalina is equally in need of Custodia's help, to extricate her from the match with Moniquito. Custodia's response is to produce Carracuca, similarly in need of a good partner. The young girl and older man are getting on well, until the jealous Moniquito catches them together and chases the pair off.
Scene 3 - The courtyard of the house. The villagers are enjoying the harvest festival, with drinking, dancing and singing. The newly enobled Juan Pedro, now accepted by Sagrario, leads the lusty Jota castellana: "Bisturí, Bisturí se quería casar" in praise of La Mancha and his marriage.
Moniquito weeps over the marriage of Carracuca and Catalina, and seeing his sorrow Juan Pedro decides he must tell Sagrario the truth about Custodia's plot. Quietly, she replies that she already knows, and that it makes no difference whatsoever to her feelings (Dúo: "Tengo una angustia de muerte".) The zarzuela concludes with a brief outburst of general delight, to the strain of the Jota: "Bisturí, Bisturí".