Inside Bartolo’s house. Bartolo is lost in thought. Might the soldier have been a spy? A visitor enters and introduces himself as “Don Alonso” (Almaviva), arriving to give the girl a music lesson in place of Don Basilio, who he says is ill. Alonso gains Bartolo’s confidence by showing him a letter written by Rosina to the Count, and offering to tell her that a mistress of Almaviva’s gave it to him, as a way to dissuade the girl from her crush. Rosina comes out reluctantly, but again recognizing “Lindoro” beneath the disguise, is suddenly delighted to sing for the visiting teacher.

Figaro enters, ready to shave and trim Bartolo, and contriving to get a key to Rosina’s balcony. But who should then appear but Don Basilio, in perfect health. Almaviva hastens the course of his illness with a quick bribe, and the others shoo him out. Almaviva whispers to Rosina that he and Figaro will come at midnight to whisk her away to wedded bliss. Bartolo overhears and, realizing he’s been tricked again, chases them all out in a fury.

Later Bartolo shows Rosina her own note, telling her the Count is merely toying with her. Rosina, thunderstruck, discloses the escape plan and agrees to marry Bartolo after all. At midnight, during a thunderstorm, Figaro and the Count arrive for the elopement, and a livid Rosina confronts them. It’s Lindoro she wanted, nothing to do with “your vile Count Almaviva.” The “vile” one reveals himself, and the three are overjoyed — but their joy turns to panic when Figaro realizes the ladder by which they entered has been moved. The doctor has foiled their escape.

A notary enters, followed by Basilio, who after another friendly financial inducement from the Count, agrees to serve as wedding witness. By the time Bartolo rushes back in, the deed is done, the girl has become a Countess and the dowry is the doctor’s to keep.