(Pasha Selim's country house by the sea, in Turkey)
The young Spanish nobleman, Belmonte, wonders how he is to enter the palace to rescue his true love, Konstanze, her maid Blonde, and his servant Pedrillo (“Hier soll ich dich denn sehen”). When Belmonte tries to get information from Osmin, the palace overseer, Osmin gives him a hard time and won’t answer his questions. Shortly after Belmonte walks away disgustedly, Pedrillo enters and asks Osmin if Pasha is back yet. Osmin gives him a hard time also, says he can’t stand Pedrillo and imagines all sorts of tortures for him. (“Solche hergelaufne Laffen”) When Osmin goes into the house, Belmonte shows up again, and he and Pedrillo have a happy reunion. Pedrillo says he will introduce Belmonte as a clever architect, and he goes to meet the Pasha. The Pasha arrives with Konstanze, whom he is wooing, but she claims her heart belongs to someone else. (“Ach, ich liebte”) Pedrillo introduces Belmonte to the Pasha, who takes a liking to him. When Belmonte and Pedrillo go to enter the palace, Osmin returns and tries to stop them, but they push him aside and enter.
(the garden of Pasha's palace)
Osmin and Blonde argue – he insists she is his slave and must obey him, she laughs in his face and orders him away. Konstanze enters, lamenting her lost love. (“Traurigkeit ward mir zum Loose”) Selim enters and insists that she must love him. She responds that she can honor him, but never love him. When Selim threatens torture of every kind, Konstanze says she will bear whatever he inflicts on her, but that she will remain faithful to her true love. (“Martern aller Arten”) After she leaves, followed by Selim, Pedrillo and Blonde enter. Pedrillo informs Blonde that Belmonte is here to rescue them; she is to inform Konstanze of the plan to escape at midnight. Her heart filled with joy (“Welche Wonne, welche Lust”), she runs off to find Konstanze. Osmin enters and Pedrillo offers him some wine. At first Osmin wonders if he should trust Pedrillo, but he gives in and drinks. The two sing happy songs to Bacchus, the god of wine, until Osmin becomes sleepy from the potion the Pedrillo slipped into his drink. (“Vivat Bacchus! Bacchus lebe!”) Osmin goes off singing. Belmonte enters, followed shortly by Konstanze and Blonde. The lovers are filled with bliss at their reunion. (“Ach Belmonte! Ach, mein Liebe!”) But Belmonte must first ask Konstanze if she loves the Pasha, while at the same time Pedrillo asks Blonde if Osmin has had his way with her. The women both become highly indignant that the men doubt their honor. The men immediately ask for forgiveness and the four sing to love.
(midnight, in the courtyard in front of the Pasha's palace)
While the four are trying to make their escape, Osmin, still half drunk, enters. He calls the guards to capture them, and is thrilled at the thought of their execution. (“O wie will ich triumphieren”) Inside, Selim is deeply offended that Konstanze has deceived him. To make matters worse, he finds out that Belmonte is the son of his bitterest enemy, who had robbed him of his position, his property and his beloved. The lovers think that they are doomed, and sing of their grief and their undying love. (“Welch ein Geschick!”) Then, to their joyous surprise, Selim informs them that he will not follow his enemy’s example; instead, he will repay injustice with good deeds by letting the four prisoners go. They are ecstatic and sign of their eternal gratitude. Osmin leaves in a rage. The others sing of Selim’s generosity and kindness – “to forgive mercifully, is a quality only of great souls!” (“Bassa Selim lebe lange”)