Act 1 - 1710 during the reign of Philip V, at the country seat of the Count of Arenal in Galicia. The Count is a bachelor who has brought up María, daughter of his deceased steward, almost as his own daughter. He has also cared for Carlos, his nephew and heir, who is currently recovering from injuries sustained in the war against Austria. The youngsters are in love, but have kept their feelings secret owing to their difference in rank.
After a brief Preludio, María and the villagers greet the Count and Carlos back from a game hunt. The old man boasts of his hunting prowess, though the groom Sebastián happily mocks his master (Introducción: "¡Ellos son!"). After the spoils are distributed, the villagers leave, and Carlos reveals that he has been ordered to return to his regiment. As soon as they are alone, he promises María to return and take her as his wife, in despite of the social stigma. They leave as the Count returns with Sebastián. He has agreed to marry the beautiful, young and wealthy Baroness of Aguafría, though it emerges they have not yet met. Sebastián offers to marry María, an idea seized on by the old man, who does not want to lose her companionship. Before Sebastián can break the good news to María, they are interrupted by the sound of a carriage overturning.
In storms the Baroness, her sumptuous dress ruined by the accident but otherwise unharmed. The villagers, with María and Sebastián, comment on the richness of her attire and invite her to stay the night whilst her carriage is repaired. Their lively bolero Coro: "Esta señora cruzaba ahora" leads into a winning Cavatina for the Baroness: "El arroyo, la enramada", with coloratura ornaments in Donizettian mode, in which she expresses her preference for sophisticated salon life, over and above the gross inconvenience of the country. She is surprised to learn that this is the estate of her fiancé, and even more surprised when she sees his advanced age. Carlos is much more to her taste, and she tries to prevent the Count's announcement of their engagement. When he finally does come out with the news, Carlos is shocked by the difference in age - and dumbstruck when the Count announces the additional engagement of María and Sebastian. The Count silences his protestations, and María - devastated by Carlos's lack of persistence - agrees to marry the groom.
The others leave, and María expresses her sorrow in a touching Romanza: "¡Ah! Yo me vi en el mundo". She is joined by the ebullient Marquis de San Esteban, dressed as a Captain of Militia and accompanied by his second-in-command Peralta, regretting that he will soon have to renounce the pleasures of the chase in favour of the uncertain delights of military service - Salida: "¡Cuál brilla el sol en la verde pradera!". The Marquis asks María for hospitality, and the three philosophise on the brevity of life's pleasures in a delicate Terceto: "Guarde Dios a la niña hermosa". The nobleman sees tears in María's eyes, but she will not tell him the cause, going into the manor house to announce his visit. Peralto is sad for his master, and decides to find some drink to drown his sorrows. He is interrupted by Sebastián, off to procure a Notary for his immediate marriage; and by the Baroness, who has decided she much prefers the idea of marriage with Carlos to life with the old Count.
When Carlos begs her to intercede on his behalf with the Count, she tells him he is worthy of something better than María. Before she can suggest herself, the Marquis blunders in and she leaves haughtily. The two men are old friends, and the Marquis is sympathetic when he learns of Carlos's difficulty. He has a plan to make all well - provided Carlos will agree to obey all his instructions without question, and leave the Estate immediately. Carlos agrees, and runs off as María comes out of the manor. When the Marquis tells her Carlos has gone without even saying goodbye she feels humiliated, and asks him to beg her guardian to place her in a convent rather than marry her off to Sebastián. The Marquis agrees, but when the Count reappears with the Baroness and Peralta, amazes everyone by asking for her hand himself. The finale begins as Sebastián returns with the Notary, and the villagers playing rustic instruments (Final: "Su rara hermosura".) He is speechless when he hears the news, María falls senseless to the ground, whilst the villagers continue celebrating the nuptials, though now for María and the Marquis.
Act 2 - A Salon in the Count's Manor House, one month later. The Baroness has been unable to leave, because of the proximity of the Austrian army. Sebastián and the villagers comment on the strange behaviour of the newly weds - husband and wife sleep apart and spend little time together (Introducción y Coro de la murmuración: "Chú, chú, chú"). María curses her fate in having a husband who cares nothing for her, and prefers instead to flirt with the Baroness. The Count storms in, determined to challenge the Marquis to a duel over his behaviour. The apparently errant husband continues to pay court to the visitor, to the Count and María's fury, whilst the Baroness herself mocks the Marquis mercilessly (Cavatina: "Blandamente murmurando") before avowing her determination not to marry the old Count.
After they have all left, Carlos returns. He is ignorant of events in his absence, and recalls his former happiness here with María in an elegant, melancholy Romanza: "Esta es la misma ventana". When Peralta tells him of María's marriage to his friend, he sees red, only to be calmed by the Marquis himself, who explains his actions. Two months ago he killed a love rival in a duel, and was condemned to death. His General, to avoid disgrace, made him swear an oath that he would die bravely in battle against the Austrians. When he has done this, María will inherit both his fortune and title, thus enabling her to marry Carlos. In proof of which, he has not touched his wife since the wedding. Carlos, moved, asks to see María, but the Marquis tells him to hide in the garden until he himself has departed for the army that night. He allows Carlos to leave a note for her on the spinet, saying he will meet her later.
Once Carlos has gone, the Marquis tries to avoid meeting María, because he has begun to fall in love with her. She reproaches him with his heartless flirtations, so to soften his wife's mood the Marquis suggests they sit at the piano and sing together - Dúo: "¡Tan! ¡tan! Niña a tu puerta", with piano accompaniment. When María discovers the note from Carlos, her nervousness affects her singing . The Marquis, struggling against his jealousy, withdraws to spy on the lovers, but when Carlos appears, María rejects his advances and tells him roundly that she now loves only her husband before leaving the room. The Marquis comes out of hiding, and bids farewell to his friend before heading off to the Army and his death. Before he leaves, he confesses his own growing love for María.
Carlos furiously reveals all to the Baroness, including the growing attachment between the new married couple. Touched, she makes him ashamed of his anger, and encourages him to behave generously towards his hapless friend and rival. He accepts her advice, and leaves with the intention of saving the Marquis and sacrificing his own life in his place. When they have gone, María rushes in, worried because her husband is preparing for "a long journey to a country from which none returns". She tries to get Peralta to recall him, but instead Sebastián appears with the news that the Marquis has already left. María tells the groom to bring her carriage and drive her after him, and he agrees in the Dúo Final: "Amor de mi alma".
Act 3 - A forest, near the Spanish army camp, late that night. A group of Soldiers sing a martial chorus in praise of the forest and leave on patrol - Introducción y Coro de la diana: "Soldados de la ronda". Sebastián and Maria come out of hiding. She is still in the dark about her husband's plans, although Sebastián feels that if he can get Peralta drunk the Sergeant will reveal all. When some officers enter with Carlos and the Marquis, María hides again. Her husband invites them all to dinner in his tent, before the dawn assault on the enemy lines. When they are alone, Carlos tries to persuade his friend to change his mind, and assures him of María's growing love. The Marquis will not hear him, and follows the other officers. Next, the Count appears, having been dragged into the forest by the Baroness, who is anxious to find María. Carlos takes them both to the Marquis's tent.
After a brief offstage Brindis (drinking song) from the soldiers, Peralta and Sebastián appear, roaring drunk on the Marquis's wine. They sing some tipsy couplets together in zapateado rhythm - Dúo: "O el mundo se menea" but Sebastián is unable to elicit any information from him. Dawn is breaking, and María herself decides to try and discover the truth from the Sergeant. Before she can try, the Marquis appears with a letter which he asks Peralta to deliver to María, and stay with her throughout the battle. The drunken Peralta refuses to leave the Captain's side, which touches his master greatly.
Maria comes forward, begging her husband not to die, and confessing her love for him. Before he can reveal his feelings, reveille sounds and he goes to leave, promising to return soon (Dúo: "Guarde Dios al gentil marido"). Suddenly Carlos rushes in, bearing a Royal Pardon. The Baroness has interceded with King Philip on the Marquis's behalf, having taken pity on the newly wedded couple's mutual love. The Marquis accepts the pardon, but still insists on giving up his wife to his friend. Finally, the Baroness herself arrives with the Count in tow. Eventually they manage to convince the Marquis that the most honourable thing is for him to admit defeat, and fall into the arms of his loving young wife. The zarzuela ends with all five expressing their content at this happy conclusion in the Quinteto Final, a brief reprise of the Terceto from Act 1.