The action takes place in Rome, at the beginning of the 19th century.A hall in the house of Don Pasquale.
Don Pasquale, a rich seventy-year old bachelor, is angry with his nephew Ernesto for obstinately refusing to marry a noble and wellto- do spinster whom his uncle has chosen for him. Ernesto is head over heels in love with Norina, a young widow of modest means. To spite his nephew the old man decides to get married himself and to disinherit the boy. Don Pasquale is impatiently awaiting his friend, Doctor Malatesta, who has promised to find him a good match. The doctor enters and begins extolling the virtues of his own sister Sofronia, a lovely, innocent creature just out of convent («Bella siccome un angelo »). Sofronia is in reality Norina, but Ernesto knows nothing of this plot woven in his favour by Malatesta, who is also a very dear friend of his. Don Pasquale is exultant («Ah, un foco insolito») and urges the doctor to introduce him to his sister without further ado. In the meantime Ernesto enters. His uncle reminds him that he has already been offered the hand of a rich spinster, warning him that, if he continues to refuse this marriage, he will find himself disinherited. Since Ernesto is irremovable, Don Pasquale orders him to leave his house, thus throwing his nephew into consternation («Sogno soave e casto»).
A room in Norina’s house.
Norina is reading a book which gives her a clue to her own character: lively, mischievous and artful, but also capable of sweetness and sincere affection («Quel guardo il cavaliere»). Meanwhile she receives a disconsolate letter from Ernesto informing her of his uncle’s decisions. Deprived of his inheritance and driven out of the house, he is heartbroken but compelled to leave her. The girl shows this letter to Doctor Malatesta, who calms her byrevealing the plan that he has devised. Norina herself shall impersonate Sofronia. With the aid of a marriage contract endorsed by the doctor’s nephew, Carlo, disguised as a notary, she will marry Don Pasquale and then reduce him to despair. The girl agrees to the trick and rehearses with the doctor the part she is to act («Pronta io son»).
Another room in Don Pasquale’s house.
Ernesto, who is about to leave his uncle’s house, once again vents his sorrow («Cercherò lontana terra») and complains of the “betrayal” of his dearest friend, Doctor Malatesta. When Ernesto has gone out, Don Pasquale receives Malatesta and a heavily veiled false Sofronia, who plays the comedy of a maiden so shy and chaste that she dare not even look at a man, though she professes an enthusiastic interest in housework. When she drops her veil, Don Pasquale is enraptured by the beauty of his betrothed. In great excitement, he hastens to sign the marriage contract, with the young Carlo acting as notary. The old man signs a certificate leaving half his estate to his wife and granting her total, absolute authority to run his household. The bride is on the point of signing when Ernesto is admitted to the ceremony. In amazement he recognizes Norina and feels perturbed and bewildered. But the doctor rapidly explains the intrigue and Ernesto, obviously pleased to support it, even agrees to be best man. No sooner is the contract signed than Norina changes her tone.Turning aggressive, impertinent and despotic, she throws her weight about in the most shameless way, doubles the servants’ wages, orders new carriages and horses, makes preparations for lavish receptions, summons dressmakers and jewellers and, worst of all, scornfully disdains the eager attentions of her husband.
The same room in Don Pasquale’s house.
Don Pasquale is distraught by the coming and going of dressmakers, hairdressers and furriers, by the exorbitant bills that keep pouring in and by the peremptory arrangements for radical changes ordered by Norina to their servants. Examining the accounts, which threaten to squander his estate, he forbids his wife to go to the theatre, but gets a loud slap for his pains. To crown matters, he picks up a letter (intentionally dropped by Norina) in which an unknown lover has arranged a rendezvous with her in the garden this evening.When Don Pasquale goes out in a fury, Ernesto and Malatesta meet to agree on other details of their ruse: the young man will sing a serenade to Norina in the garden and then hide. Don Pasquale returns looking despondent, by now bitterly regretting his marriage and longing to be released from it. Malatesta, exhorting him not to raise a scandal, advises him to surprise the lovers and to repudiate Sofronia if he can catch her redhanded («Cheti cheti immantinente»).
A copse in the garden next to Don Pasquale’s house.
Don Pasquale and Malatesta take up their positions among the trees while Ernesto, pretending to be Sofronia’s unknown lover, launches into a serenade («Com’è gentil»). Norina approaches and they exchange tender effusions («Tornami a dir che m’ami»). The doctor and Don Pasquale come out of their hiding-places and catch Norina in the act. Ernesto, who had hurriedly vanished from the scene, now re-enters the garden as if by chance. Advised by Malatesta, Don Pasquale triumphantly announces to the false Sofronia, in order to rouse her anger and induce her at last to leave his house, that he intends to welcome back Ernesto. Moreover he will permit him to marry Norina who will thus take over as the new lady of the house. At this point the plot against him is revealed and the old man is delighted to be freed from the redoubtable Sofronia. With his usual affectionate «Ah, bricconissimi», he forgives them all and blesses the marriage of Ernesto and Norina.