The servants at Chérubin’s chateau are preparing the celebration of the young man’s first military commission and his seventeenth birthday, while Nina confesses to Chérubin’s tutor Jacoppo (Le Philosophe) the affection she has held for his pupil since childhood, even though he now ignores her. The Duke, Baron and Count have learned that Chérubin has invited the celebrated premiere danseuse of the Teatro Real, Madrid, L’Ensoleillad, to come and dance that evening. As the three jealous men ridicule the handsome, dashing Chérubin, he declares his happiness because L’Ensoleillad has accepted. While peasants dance and entertain, the guests watch the festivities on the terrace, and Chérubin tells the entranced Countess he has left a letter for her in the hollow of an old willow tree. The Baroness, too, is taken with the boy. Finding his pupil melancholic, Le Philosophe asks why he is so downcast, and the young man confesses that he cannot look at a woman without becoming amorous, sick with love. The elder tells him it is only natural. In a fury, the Count has intercepted the letter Chérubin has penned to his wife and wants to challenge him to a duel, but the innocent Nina pretends the verses were meant for her and proves it by reciting the madrigal by heart. Although the Count is satisfied, the Countess is irked to learn Cherubin loves Nina. Le Philosophe delights in knowing his pupil loves the girl he himself has chosen for him. Chérubin excitedly proclaims he loves a ravishing creature – not Nina, but L’Ensoleillad, who arrives with pomp and ceremony.

In the courtyard of the inn, travelers are trying to get rooms for the fiesta, and when the Baroness and Countess are shown to their small quarters they pronounce them unworthy of their station. The Innkeeper reveals the best ones are reserved for L’Ensoleillad, the favorite of the King. Some officers and their girlfriends (manolas) celebrate their new companion in the regiment and, despite his dashing uniform and plucky manner, are surprised at his diminutive stature. When Chérubin makes a pass at Ricardo’s mistress, the outraged Captain challenges him to a duel. A masked woman arrives, and Chérubin brashly embraces her and gives her a rough kiss – but he apologizes when she is revealed to be L’Ensoleillad. Le Philosophe pleads with Ricardo to excuse Chérubin because of his youth and inexperience. Ricardo calls off the duel, and L’Ensoleillad, who had fainted in the fracas, recovers, rebukes the men, offers a toast to love and launches the fiesta by dancing. Le Philosophe warns Chérubin to be on guard against the dangers incurred by such an amorous life, but the young man, longing only to see L’Ensoleillad appear on her balcony on such a beautiful evening, sends the exasperated tutor away. Chérubin finally catches sight of the dancer and sings to her. Delighted, she comes down to him, and the two lovers, lost in their blissful private words, vanish into the nearby woods. The Baron, Count and Duke decide to thwart Chérubin’s attentions to L’Ensoleillad because of the King, but the returning lovers lead them on a merry chase. Chérubin draws the men into the woods so L’Ensoleillad can return to her room without being caught. Quickly returning, he finds a ladder, climbs it and embraces the dancer through the bars of her balcony. The duped men burst on the scene, and Chérubin has just enough time to leap down and mockingly throw the ladder to the ground, making it impossible for them to know at which lady’s window he was. The love-tokens of a bouquet, a ribbon and a garter – from the Baroness, Countess and L’Ensoleillad respectively – add to the confusion. Chérubin parries with the outraged men before the police arrive to order the noblemen’s arrest for inciting a riot, and the women faint.

The next morning on the inn’s court yard, Chérubin, preparing for three duels, draws up his will, but the Baroness and the Countess demand to know to whom he was singing the previous night. As he admits it was L’Ensoleillad, their husbands return and heap reproaches on Chérubin. The women assure their husbands it was not them whom Chérubin visited but L’Ensoleillad, and so any question of a duel is past. The Duke delivers a royal message to the dancer, who, summoned back to court, leaves while extolling the virtues of one night of fleeting love. Chérubin tries to detain her, but left alone with Le Philosophe he gives rein to his disillusionment, cursing love. His tutor advises him to wait for true love, “a woman who is kind and understanding, one who will console you in adversity.” Just then Nina comes to take leave of Chérubin before retiring to a convent because of unrequited love. As the young man realizes he is the cause of her sorrow, he begs forgiveness, and Nina is moved by his sincerity. The pair declares eternal love, as Le Philosophe orders Chérubin to be rid of the Countess’ ribbon sticking out from his contrite pupil’s coat . He does so and rushes into the arms of his forgiving Nina.