Mid-day.

The Countess, alone in her apartments, longs for the love she and her husband once enjoyed. Susanna comes to tell her of the Count’s unwanted attentions. Figaro joins them and presents his plan to trap the master: Figaro has sent him an unsigned note, by way of Basilio, revealing an assignation between the Countess and an admirer, fixed for that evening in the garden. He advises Susanna to pretend to accept the Count’s invitation to a tryst — and to send Cherubino (who has yet to leave for the army) in her clothes, in her place. The ladies, delighted, lock the door and commence costuming; but the arrival of the Count interrupts them and the panicked Countess hides Cherubino in the dressing-room. The Count shows his lady the mysterious note, hears a sudden sound, sees the Countess’s unease, tries to force the door, is dissuaded, demands the she escort him to fetch the necessary tools to open the closet … while Susanna slips in to take Cherubino’s place and the unluckily lucky boy leaps out the open window into the hedgerows. Returning, the Count is astonished to see Susanna, and not the hated page, step calmly from the wardrobe. The Countess is vindicated and the Count begs her pardon — though not before chastising her for such a cruel joke. Figaro enters to say the ceremony is prepared and awaits the celebrant. The Count filibusters. The gardener Antonio blusters in having just seen a man jump from above and hit the ground running. Figaro covers for the page, hopping to identify himself as the jumper. Then Marcellina and Bartolo bring their grievance and its attendant documentation, demanding the Count settle the score and marry Marcellina and Figaro.

Afternoon.

Almaviva considers the recent events. Susanna pops in for a flask of smelling salts for her mistress and, to his surprise, stays to make a date. Overhearing her whispering to Figaro on her way out, he realizes he’s the victim of a trick, and swears revenge. Meanwhile, Barbarina takes a nervous Cherubino back to her house to disguise him. An anxious Countess waits for Susanna to plan their own disguise: she herself, and not Cherubino, will meet the Count in Susanna’s clothes.

Don Curzio brings Marcellina’s case before the Count, demanding that Figaro pay up. But seeing the unusual tattoo on his arm, she and Bartolo recognize him as the fruit of their long-ago love. Not his bride and her defender, then, but his mother and father … everyone is overjoyed! Everyone except the Count, who now, with Figaro’s debt forgiven and the additional wedding of Marcellina and Bartolo to celebrate, must rethink his own plans.

The Count is sure Cherubino has left for Seville, but Antonio enters insisting that the boy is still on the grounds. Improvising on Figaro’s strategy, the Countess dictates a note to Susanna inviting the Count to the garden that evening. They seal it with a pin, to be “returned to sender.” A chorus arrives, containing one conspicuously awkward bridesmaid, and sings to the Countess, as Susanna kneels before the lord of the manor and slips him the note, on which he pricks his finger. The Countess recognizes Cherubino, and the Count soon does too. At the boiling point, he is outwitted by Barbarina, who asks to have the page for her husband.

Evening.

Barbarina has been outwitted by the pin that pricked the Count. Figaro and Marcellina find her looking frantically for it, and she tells them the Count expects her to return it to Susanna. His suspicions fully kindled, Figaro turns to his mother, who reminds him that all the strategic strata are surely not yet known — and who, when he storms away “to avenge all husbands,” hastens to inform her former rival, now daughter-to-be, Susanna. Barbarina hides in the pavilion. Susanna and the Countess trade cloaks in the cooling air, and the Countess hides in the pavilion. Susanna, warned by Marcellina that Figaro is hiding in the dark, revels for a delicious instant in the knowledge that he’s listening. Cherubino enters in search of Barbarina, and finding “Susanna,” tries to seduce her — until the Count arrives for his own assignation and throws the lad out. While he attends in earnest to “Susanna,” the woman he thinks he’s found is found out by her own husband. Figaro has recognized Susanna’s voice, and he joins the joke by playing a grand love scene with his “Countess” for an audience of Almaviva. The Count’s jealousy explodes. While he is shouting down his servants’ cries for mercy, the Countess steps out to reveal herself. The Count is thunderstruck. He begs her forgiveness. The couples are reunited, and this mad day rolls to a close.