Background The young Spanish nobleman Belmonte has suffered having his betrothed, Konstanze, her English maid, Blonde, and his servant, Pedrillo, all kidnapped by pirates and sold to Selim Pasha. The Pasha, who was not born a Turk but instead as a Spanish Christian who later converted to Islam, has fallen in love with Konstanze and has had her and the other captives brought to his country estate.
Act I After somehow finding out where his beloved and her companions are being kept, Belmonte has arrived to free them. Although the wrathful harem overseer, Osmin, attempts to drive him away, Belmonte still succeeds in meeting with Pedrillo to discuss what to do. The Pasha arrives with Konstanze, whom he is still showering with love. The girl, however, frankly declares that she will never love anyone other than her lost fiancé. Meanwhile, despite all of Osmin's efforts, Belmonte has entered the palace with help from Pedrillo.
Act II The merry little maid Blonde is not the least bit afraid of her irate slave-master. Although the pasha has made a gift of her to Osmin, in reality she's the one who controls her master, not the other way around. With an aching heart, Konstanze remembers the happy times before fate separated her from Belmonte. The pasha arrives. He warns the unfortunate girl that his patience has come to an end: if Konstanze will not submit to his courting, then he will not shrink from torture. However, Konstanze is strong and determined ("Tortures of every kind may await me") and cannot be swayed from a decision once she has made it. Then Pedrillo tells Blonde the great news. Before the maid rushes off to inform Konstanze, she and her sweetheart quickly concoct a plan for how to get the ever-alert and suspicious Osmin out of the way. Soon enough, Osmin appears and immediately notices what an unusually cheerful mood Pedrillo is in. Pedrillo doesn't lose any time coming up with an explanation: a little bit of fine old wine can soon make even the harshest servitude seem better. Osmin cannot resist the temptation for long. He takes heartier and heartier gulps from the wind until finally passing out. Evening comes and the two couples happily prepare for their escape. Act III Nevertheless, the escape is not successful. At just the wrong time, Osmin awakes. Suddenly sober, he calls the guards, and the soldiers seize the absconders. The fugitives are dragged before the Pasha, who realises from Belmonte's words that he has the son of his deadly enemy, the man who ruined his life, in his power. Although the young people suspect that mercy will not be forthcoming, they anticipate death calmly in the knowledge that they will never be separated from each other again. The Pasha, however, overcomes his thirst for revenge: he gives up his pursuit of Konstanze and sets them all free.