Echegaray's play is successful enough on its own terms - swift, witty and neatly characterised - but the abiding delight of La viejecita is Caballero's brief score, one of his last and best. Much of it had to be dictated due to the composer's encroaching blindness, but he put together a delicious confection of old-fashioned elegance and subtle humour. The Old Lady's song "Al espejo al salir me miré" is particularly effective, gently touching as well as humorous in context; whilst the Minuetto and the duet "¡Pobre viejecita! ¡Qué delicadita!" are equally memorable and personal in style.
It seems that Echegaray originally intended Carlos for a male performer, but that Caballero tailored it to the talents of the mezzo soprano Lucrecia Arana, who later created the role of Pilar in Gigantes y cabezudos. Whatever the original circumstances, there is no doubt that this particular 'breeches' role is best played these days by a tenor - a solution which makes as much sense musically as dramatically. Much of the farcical fun and character of La viejecita is lost when Carlos 'in drag' is in reality a soprano out of it!
Scene 1 - The Officers' Mess of a Spanish artillery barracks, in 1812. After a brief Preludio largely based on the later Minuetto, the curtain rises to reveal three hussars, Federico, Fernando and Carlos, enjoying several bottles of wine with their fellow officers. They launch into a lively brindisi (Introducción y brindis: "Ya estoy tranquilo ... Para morir de amor ciego"). Fernando has received a letter from Mexico with news that his rich aunt Doña Teresa de Argelez y Vargas is due to return home to the mother country. As soon as Fernando and Carlos are left alone, the latter confesses to his friend that he is in love with Federico's fiancée Luisa, daughter of the Marquis of Aguilar, who views him as an irresponsible good-for-nothing. That night the Marquis is holding a ball at his palace, and Carlos is determined to use the occasion to make love to his sweetheart.
However, when the officers' invitations arrive, Carlos has been specifically excluded, which makes him the butt of the soldiers' humour. (Coro de la invitación: "Pobrecito Carlos ... En un cerillo se alza un palacio"). Thoroughly riled, Carlos makes a bet with them - he will gain entry to the party, hug Luisa three times, and fight a duel with Federico. Only Fernando and Sir George, an English Captain in the Allied army, take his side against the mocking officers. The wager is sealed with a handshake and all agree to meet at the Marquis's mansion that night.
Scene 2 - The ballroom in the Marquis' house. Final preparations for the ball are in train. The Marquis is talking to his brother Don Manuel, a good-humoured buffoon, when Luisa comes down. Don Manuel knows that she is in not in love with Federico, but his attempts to take her part and speak up for Carlos fall on stony ground - the Marquis refuses to listen to a word he says. Luisa defends Carlos stoutly - agreed, he has exhausted his family fortune in double-quick time, but that is down to his unwordliness and the lack of a good woman by his side. Softened by his daughter's plea, the Marquis agrees to reconsider the situation, provided Carlos commits no more acts of idiocy. The civilian guests arrive to the strains of a mazurka, followed by a company of English dragoons - led by Sir George - who praise Luisa's beauty in a insouciant choral Schottisch (Mazurca y Chotis de los Dragones Ingleses: "Como en correcta formación".)
When the officers arrive without Carlos they understandably think they have won the bet. Then the arrival is announced of Doña Teresa de Argelez, from Mexico. The little Old Lady - Carlos in disguise - is received with great courtesy by the Marquis and his guests, though the baffled Fernando certainly does not recognise her as his aunt. La viejecita sings of her past amorous triumphs in a wistful little song (Canción de la viejecita: "Al espejo al salir me miré") joined by the entire company. She soon strikes up a friendship with Luisa, detaching her firmly from the luckless Federico, and Fernando at length realises just who this 'aunt' really is.
He asks Carlos to dance, but Don Manuel sweeps la viejecita into the centre of the floor to lead the Minuetto, during which she makes a lot of clodhopping gaffs which eventually cause the dance to grind to an unseemly halt. Next, the Old Lady makes a beeline for Luisa. Praising her youthful beauty, she squeezes the girl three times - Sir George meanwhile counting the precise number of hugs out loud. As soon as the officers are left alone Carlos reveals his identity and Federico, furious, challenges him to a fight there and then. Sir George steps between them, but when Don Manuel comes in to see what all the noise is about, he is amazed to find the Old Lady with sabre in hand, and shouts to his brother. Carlos quickly pretends to feel faint, and the thoughtful Marquis leaves the unfortunate viejecita to Luisa's quiet ministrations.
As soon as they are alone, Carlos reveals his identity, causing Luisa to nearly faint in her turn, but he is swiftly forgiven in a touching duet (Dúo: "¡Pobre viejecita! ¡Qué delicadita!") Fernando tells Carlos it is time to leave, now he has nearly won the bet, before the Marquis's suspicions are fully aroused. Carlos leaves to duel with Federico. The Marquis quizzes Fernando on the peculiar habits of his relation; but soon the Old Lady returns wiping a sabre clean, having beaten Federico by drawing first blood. She still has enough presence of mind to plead with the Marquis - to such charming effect, that he agrees to forgive Carlos if the young man shows willing to settle down and stop playing the fool. Carlos tries to discreetly lose his dress, but is spotted by the enamoured Don Manuel, who chases la viejecita round the ballroom and up to the gallery. The Marquis asks his daughter why she is so miserable. Luisa tells him that it is because of his refusal to invite Carlos to the ball. When the contrite young officer appears in full dress Hussar's uniform to beg the Marquis's pardon for past sins, Luisa's father readily forgives him. He must bid them farewell, as the army returns to the front at dawn, but Carlos promises Luisa he will return alive to claim his bride.