Act I
Rome, 1800. Cesare Angelotti, an escaped political prisoner, rushes into a church to hide in one of the chapels. Once he has disappeared, a sacristan enters and then the painter Mario Cavaradossi, who sets to work on his portrait of Mary Magdalene. The painting has been inspired by the Marchesa Attavanti, whom Cavaradossi has seen in the church but does not know. While he works, he compares the dark-haired beauty of his lover, the singer Floria Tosca, to that of the blonde Marchesa Attavanti (“Recondita armonia”). Angelotti, a member of the former Bonapartiste government, ventures out and is recognized by Cavaradossi. The painter gives him food and hurries him back into the chapel as Tosca is heard calling from outside. Suspicious, she jealously questions Cavaradossi, then reminds him of their rendezvous that evening at his villa. Suddenly recognizing the Marchesa Attavanti in the painting, she accuses him of being unfaithful, but he assures her of his love. When Tosca has left, Angelotti emerges from the chapel. A cannon signals that the police have discovered the escape, and he and Cavaradossi flee to the painter’s villa. The sacristan enters with choirboys who are preparing to sing in a Te Deum that day celebrating a victory against Napoleon. Their excitement is silenced by the arrival of Baron Scarpia, chief of the secret police, who is searching for Angelotti. When Tosca comes back looking for Cavaradossi, Scarpia shows her a fan with the Attavanti crest that he has just found. Seemingly finding her suspicions confirmed, Tosca bursts into tears. She vows vengeance and leaves as the church fills with worshipers. Scarpia sends his men to follow her to Cavaradossi, with whom he thinks Angelotti is hiding (“Tre sbirri… Una carozza…”). While the congregation sings the Te Deum, Scarpia declares that he will bend Tosca to his will.
Act II
Alone in his palace, the Palazzo Farnese, Scarpia sadistically anticipates the pleasure of having Tosca in his power (“Ha più forte sapore”). The spy Spoletta arrives, explaining that he was unable to find Angelotti. Instead he brings in Cavaradossi. While Scarpia interrogates the painter, Tosca is heard singing at a royal gala in the same building. Scarpia sends for her and she enters just as Cavaradossi is being taken away to be tortured. Frightened by Scarpia’s questions and Cavaradossi’s screams, Tosca reveals Angelotti’s hiding place. Cavaradossi is carried in, hurt and dazed. Realizing what has happened, he angrily confronts Tosca, when the officer Sciarrone rushes in to announce that, in a surprise, Napoleon has won the Battle of Marengo, a defeat for Scarpia’s side. Cavaradossi shouts out his defiance of tyranny and is dragged off to be executed. Scarpia, calmly resuming his supper, suggests to Tosca that he would let Cavaradossi go free if she’d give herself to him. Fighting off his advances, she calls on God and declares that she has dedicated her life to art and love (“Vissi d’arte”). Scarpia insists, when Spoletta interrupts: faced with capture, Angelotti has killed himself. Tosca, now forced to give in or lose her lover, agrees to Scarpia’s proposition. The baron seemingly orders a mock execution for Cavaradossi, after which he is to be freed. Spoletta leaves. As soon as Scarpia has written a safe-conduct for the lovers, Tosca kills him with a knife she had found earlier on the table. Wrenching the document from his hand, she quietly leaves the room.
Act III
At dawn, Cavaradossi awaits execution at the Castel Sant’Angelo. He bribes the jailer to deliver a farewell letter to Tosca. Overcome with memories of love, he gives in to his despair (“E lucevan le stelle”). Tosca enters. She explains to him what has happened and the two imagine their future in freedom. As the firing squad appears, Tosca instructs Cavaradossi how to fake his death convincingly, then hides. The soldiers fire and depart. Tosca urges Cavaradossi to hurry, but when he doesn’t move, she realizes that Scarpia has betrayed her and that the bullets were real. Spoletta rushes in to arrest Tosca for murder. She cries out to Scarpia and leaps from the battlement.