Figaro explores territory that many found worrisome when it was written in the mid-1780s — the often contentious relationship between the classes. That's why the original play by Beaumarchais was banned by ruling authorities in France, and why Mozart's opera made the Austrian monarchy more than a little bit nervous. Both the play and the opera clearly illuminate the limitations of rank and privilege, showing that common sense can readily overcome wealth and power, and that genuine humility easily upstages unwarranted arrogance.

Beaumarchais’ play, The Marriage of Figaro, is a sequel to his earlier play, The Barber of Seville, (basis for Rossini’s opera) in which a young nobleman named Almaviva won his lover, Rosina, away from her lecherous guardian, Dr. Bartolo — but only with considerable help from his friend Figaro. As The Marriage of Figaro begins, three years have passed. The young lovers are now the Count and Countess Almaviva. Figaro is the Count's personal valet, and he's engaged to marry the Countess' maid, Susanna.

The story is set in Spain. Figaro is jealous of the Count for his gallantry to Susanna, his betrothed. The Count, sensing that the page, Cherubino, is interested in the Countess, seeks to get rid of Cherubino by ordering him off to the wars. He is saved by Susanna, who disguises him in female attire.

The Countess, Susanna, Figaro and Cherubino conspire to punish the Count for his infidelity. The latter suddenly appears at his wife's door. Finding it locked, he demands an entrance. Cherubino, alarmed, hides himself in a closet and bars the door. When the Count goes after a crowbar to break in the door, Cherubino leaps out of the window, while Susanna takes his place. Antonio, the gardener, comes in, furious that some one has just thrown a man into his flower pots. Figaro at once asserts that it was he who jumped. A ludicrous side plot unfolds as Marcellina appears with a contract of marriage signed by Figaro, bringing Bartolo as a witness. Don Curzio declares the contract valid. Figaro stalls by protesting that he can't marry her because he's actually a nobleman, stolen from his parents at birth. He displays a distinctive birthmark on his arm. Marcellina recognizes the mark, and nearly faints. It turns out that Figaro is her and Bartolo’s long-lost illegitimate son. Figaro is off the hook and he and Susanna are free to be married at last. Bartolo and Marcellina decide to make it a double wedding.

That night, in the garden, the servant girl, Barbarina, is searching for something in the dark. Though she's barely a teenager, she has already been the object of the Count's attentions. Now she's acting as a courier between the Count and her older cousin Susanna, who has just been married. Figaro is convinced Susanna is plotting to betray him, especially when he hears her nearby, singing about her "lover" — though she's really singing about Figaro. Things come to a head when the Count finally shows up, eager for his tryst. First he tries to seduce his wife, thinking she's Susanna. Then, when he sees Figaro with a woman he thinks is the Countess, he self-righteously accuses her of infidelity. Susanna, still imitating the Countess, begs the Count for forgiveness. He refuses. At that, the Countess reveals herself, and the Count realizes he is trapped. Humbled and repentant, it's his turn to ask for pardon. The Countess generously embraces him, and the opera ends with both couples reconciled.