Don Pasquale has demanded that Ernesto break up with Norina, his penniless widow of a girlfriend, and marry a woman Don Pasquale has chosen. But Ernesto refuses because he and Norina truly love one another. To teach the young rascal who’s the boss, Pasquale decides to disinherit Ernesto and get married himself. Dr. Malatesta, foreseeing disaster, takes matters into his own hands and asks Don Pasquale to let him choose the bride. He explains he has a budding flower of a sister in a convent and means to introduce her to Don Pasquale. The old man is delighted, and so Dr. Malatesta starts to lay his trap.
Later that morning at Norina’s house, the doctor tells her she must play the part of Sofronia, his sister, and he has enlisted his cousin Carlotto to help arrange a phony marriage. Back at Don Pasquale’s house, Norina acts meek and submissive when she meets the old man, and he "weds" her at once. But no sooner have they signed the (fake) marriage certificate than she changes character: now she makes the old man’s life a living hell by spending a fortune, planning an excursion to the theater without him, bossing Don Pasquale around, and even slapping him when he steps out of line. Just when Don Pasquale thinks he’s about to catch her in flagrante delicto with a paramour in a nighttime assignation in the garden, Dr. Malatesta’s plot comes to a head, Don Pasquale learns an important lesson, and young love triumphs.