June 1800, the Sant’ Andrea della Valle church in Rome. A man bursts in and, after a desperate search, finds a hiding place that has been prepared for him in the Attavanti family’s chapel. The sacristan brings brushes, paints and something to eat for Mario Cavaradossi, who's working on a painting of Mary Magdalen. The sacristan thinks he recognises a woman, who's been seen praying in the church recently, in the saint’s features; Cavaradossi says he's right and broods over the different manifestations of feminine beauty: the blonde Countess Attavanti (Angelotti’s sister) and his black-haired lover, the opera singer Floria Tosca. The fugitive, believing he is alone, emerges from his hideout. Cavaradossi sees that it's Angelotti, consul of the overthrown Roman Republic, and offers his help. At that very moment Floria Tosca knocks loudly on the church door. Cavaradossi, not wanting to take any risks, decides not to let her know about the prisoner’s escape. He tells Angelotti to hide again and gives him the basket of food. Tosca suspects that Cavaradossi has been meeting another woman; he tries to appease her jealousy. She suggests they spend the evening together after her performance at the opera but his thoughts are elsewhere, and his lukewarm reaction rekindles her jealousy. She recognises Attavanti’s face in the painting and feels that her suspicions are justified. Cavaradossi eventually manages to calm her down and persuade her to leave; she demands that he paint Mary Magdalen’s eyes black. Cavaradossi gives Angelotti directions to a hideaway. The boom of a cannon announces that Angelotti’s escape has been discovered. There's no time to lose; Cavaradossi will take Angelotti to his home, where the Republican can find refuge. The sacristan brings news to the choristers about the Austrians’ victory over Napoleon’s army and orders that preparations be made for a celebration. The singers rejoice. Baron Scarpia enters with his thugs and is outraged about the disorder in the church. The intimidated sacristan is questioned; the secret police find Angelotti’s clothes, the empty basket and a fan belonging to Attavanti in the chapel. Suspicion falls on Cavaradossi. Tosca returns; she must cancel her date with her beloved because she's to sing at the celebrations. Scarpia feeds the flames of her jealousy by saying he found the fan on the painter’s scaffolding. Tosca hurries off to Cavaradossi’s house, unwittingly leading Scarpia’s spies to where they think Angelotti's hiding. While the choir sings Scarpia indulges in fantasies of lust and power. ACT II The Palazzo Farnese. Scarpia has sent for Tosca. The police informer Spoletta reports that the search for Angelotti was futile. Only Cavaradossi was arrested and brought in for interrogation, but he's giving nothing away. A celebratory cantata, with Tosca as soloist, can be heard through the window. Scarpia orders that Cavaradossi be tortured. Tosca enters just as the painter's being taken away; Cavaradossi begs her to say nothing. She assures Scarpia that her jealousy was unfounded. She's horrified when Scarpia tells her that her lover's being tortured. Cavaradossi manages to remind Tosca to say nothing, but she can’t bear hearing his cries of pain any longer, and tells Scarpia where Angelotti's hiding. Cavaradossi is brought in unconscious. Scarpia sends Spoletta to get Angelotti. Sciarrone brings the surprising news that reports about the battle near Marengo were misleading, the battle turned and Napoleon was victorious. With his remaining strength Cavaradossi errupts in jubilation, provoking Scarpia; he's led away, his fate seems sealed. Tosca tries to negotiate a »price« for Mario’s release with Scarpia, who's known to be corrupt; but, to her horror, Scarpia demands physical remuneration instead of money. Tosca realises she has no choice. She reflects on her life and artistry. Spoletta reports that Angelotti has killed himself. Scarpia forces Tosca to make a quick decision; she agrees to the deal. Scarpia gives orders that Cavaradossi will be subjected to a sham execution by firing squad, and writes out a permit for Tosca and the painter to leave the city after the feigned execution. When Scarpia attempts to embrace her Tosca makes a lightning decision, grabs a knife from the table, and stabs him. ACT III The roof of the Castel Sant’ Angelo. The song of a young shepherd can be heard in the distance. Mario hands over his last possession to the prison warder in order to be allowed to write a farewell letter to Tosca. His thoughts before dying are only about her. Tosca brings news about the feigned execution and tells him how she murdered Scarpia. Both vacillate between apprehension and hope for the future. Tosca tells Mario that he must play dead after the shots have been fired, until the soldiers have left. The firing squad shoot, and Mario falls. As agreed, Spoletta prevents the sergeant from giving him a coup de grace. But, when all have gone, Mario doesn't move. He really has been shot. Soldiers hurry to the platform: Scarpia’s body has been found, Tosca obviously his murderer. Before she can be seized she leaps from the castle to her death.