Serrano's score is as polished as the libretto, which isn't to say that it lacks feeling. Quite the reverse! As ever, Serrano responded to a nocturnal, Italian setting to produce top-drawer work. The set-piece songs and choruses of the first two scenes would surely have been reason enough to make this score a classic, but in the extended duet which comprises the whole of the third scene Serrano managed an integration of music and drama that he never surpassed. The themes of the "Canción del olvido" itself and Leonello's "Mujer, primorosa clavellina" are deployed to great theatrical effort; the Soldiers' Chorus is if anything more popular than either; and who could forget the delicate tone-painting of the Preludio, the piquant scoring of the Intermedio before the last scene? Composer and librettists succeeded brilliantly in their work, and the result is a great romantic zarzuela, unpretentious but richly durable, the Apotheosis of the Serenade.
Scene 1 - The action takes place in Sorrentinos, a fictitious city in the Kingdom of Naples, 1799. A square in the town, the Goose Inn on one side, the palace of the courtesan, Flora Goldoni, on the other. It is dusk. After a delicate Preludio the curtain rises. The middle-aged Sainati is loitering in hope of a glance from the famous courtesan, but the Innkeeper tells him he has too many rivals - if he wants a chance, he should first get rid of his wife! Sainati slinks away, as a poor Roman musician - Toribio Clarinetti - parks himself outside the inn with his harp. He has been paid to serenade the guests, and demands a meal from the Innkeeper, who asks him about a mysterious young woman who is lodging there. Toribio blusters, but soon the woman herself appears. She is Rosina, a young Roman Princess, rich and beautiful. Despite the fact that she owns the nearby Marinelli Palace, she is lodging at The Goose in pursuit of a secret plan to attract a certain Captain Leonello, with whom she fell in love in Rome, though as yet he does not even know of her existence. The maid Casilda warns her that as the Captain fancies himself as a Don Juan her mistress is heading for disaster, but Rosina is utterly determined to pursue him.
Leonello arrives at The Goose with two friends, Pietro and Paolo, to enjoy a bottle of wine. Rosina, listening through the lattice of her room, overhears as he coolly recounts the story of his first meeting with the beautiful courtesan who lives opposite, and his confident plans to enjoy her (Canción: "Junto al puente de la Peña".) When the Innkeeper tells him that one of the lady guests has been asking about him, he replies that she can have him, when he's done with La Goldoni - perhaps even for a couple of days! All this only makes Rosina desire him the more. Leonello tells his friends that he has commissioned his company Sergeant, Lombardi, to provide some musicians to sing a serenade whilst he recites sonnets by Petrarch to win La Goldoni's favours. When he spots Flora on her balcony across the square, he tells Toribio to sing a song - any song. The musician chooses a Roman favourite, the Canción del Olvido ("Song of Forgetting") and launches into the introduction on his harp; but as he opens his mouth to sing, another voice - Rosina - takes up the melody herself. Leonello and his friends are captivated by the sound of the beautiful, mysterious voice (Canción del Olvido: "Marinela".)
Leonello swiftly comes to his cynical senses ... just like a woman. Another one in love with the moon! Sergeant Lombardi reports that no musicians are to had, but that the soldiers themselves are willing to stand in. As his friends leave with Lombardi to hear their serenading, Leonello goes into the shadows to write a passionate love letter to La Goldoni. Rosina has her own plan, for which she needs Toribio's help. In return for 3,000 Guilders and the clothes he is to play Rosina's husband, "The Prince of Ferratta" and pretend to be in love with the Courtesan. After a little comical priming he is just about fit to play his part, though he jibs at the idea of the Princess acting as his page. Another 500 Guilders remove that objection and Toribio, chuckling over his luck, goes into The Goose with Rosina. Leonello finishes his letter, but before he can rush away to join his friends he hears once again the voice of the mysterious woman in her Song of Forgetting. The pages of the love letter fall to the ground. Leonello stands transfixed as the curtain falls.
Scene 2 - a nearby street, by moonlight. On one side is the Goldoni, and on the other the Marinelli Palace. A group of musicians are heard singing (Coro: "Ya la ronda llega aquí") and one of them addresses a serenade to Goldoni (Serenata: "Hermosa napolitana"). Toribio is revelling in his Princely role, and gets ready to sing his own serenade to Flora. Leonello, anxious that Lombardi and his soldiers will not show up, takes the absurd musician for a rival and offers to fight him. Frustrated by Toribio's verbal wriggling, Leonello leaves him, and "The Prince" runs off in the opposite direction, leaving his "page" to perform his serenade to mandolin accompaniment (Canción: "Canta el trovador".)
Flora Goldoni opens her window and asks the page for whom he is singing such a lovely song? Rosina's gracious rhetoric on behalf of her master charms Flora into receiving the Prince; and though Torisio does his best to put his foot in his mouth, Flora accepts the Page's excuses for his eccentric behaviour and agrees to receive him in her house. After some further priming on polite behaviour, he enters the Goldoni Palace, just before the soldiers finally march in with Lombardi, playing their bandurrias and singing their robust idea of a serenade (Coro y solo: "Soldado de Napolés") before heading back to barracks.
Leonello swaggers in confidently. The Page tells him that his master the Prince of Ferratta is already with Flora, and that he has missed his chance. The Captain threatens to run The Prince through, but the page mocks his lack of subtlety. "How little you know of love," he laughs. "Use your wits, and not brute force." Impressed in spite of himself, Leonello offers the lad 500 Guilders for some advice. Well then, says Rosina, why not enjoy himself with the Prince's wife? That will be the perfect revenge, and make Flora jealous into the bargain. The Marinelli Palace is just over the way, but how will he get in? The page tells him to arrive punctually at ten o'clock, sing a serenade, and leave the rest to him. Leonello leaves to ready himself, a second before Toribio gets thrown ignominiously out by La Goldoni. Rosina calms him down, and after a poetic apostrophe to the night she listens quietly as the sound of the serenade is borne in on the evening breeze (Voz interno: "Hermosa napolitana").
Scene 4 - The Princess's garden, at night, two weeks later. A subtly scored Intermedio suggests the passage of time before the curtain rises. Toribio, still disguised as the Prince, is giving a large party and telling risqué stories to the guests, including Leonello's friends Piero and Paolo. His "wife" and Leonello are nowhere to be seen, which ought to worry the Prince - although it doesn't seem to. On cue, in comes the Princess with Leonello to confirm their suspicions. Two weeks have effected a huge difference in the Captain, no longer interested in anyone except this "married woman", and well prepared to defend her honour against Piero's snide remarks. She has told him she loves him, but will not compromise her honour, so he must suffer nobly. Wouldn't it be better to finish the business by killing her silly old husband in a duel? Having planted this idea, his friends leave to enjoy the regatta the Princess has provided for their amusement.
The "Prince" appears, and is horrified when Leonello offers to fight a duel on the spot. He tries to talk his way out of it, but before matters can come to a head Rosina appears and asks Leonello what he thinks he is doing? She mocks his machismo posturings, and tells him laughingly that only in suffering can he find true love. He protests that his days as a Don Juan are over, and in despair challenges her to deny the one thing she has said to keep his hope alive - that she would never forget his love. At last she softens, and falls into his arms (Dúo final: "Pero, capitán ...".) To Leonello's confusion, in rush the guests with Toribio and the Captain's friends, Rosina's plot is swiftly explained - and the loyal Toribio is rewarded with the post of Major Domo. Everything has been a charade - except of course for Rosina's true love for Leonello, and his for her.