June 1800. Italy has long been under the domination of the Hapsburg dynasty. Napoleon Bonaparte, however, has emerged as a threat to the status quo and Rome is in chaos, without a clear ruler. Baron Scarpia, the chief of police, has become the highest authority. Loyal to the King and Queen of Naples, Scarpia seeks to eliminate any remaining trace of Napoleon's attempts to establish a secular Roman Republic.
ACT I: THE CHURCH OF SANT'ANDREA DELLE VALLE
Cesare Angelotti, a Republican, has just escaped from the Castel Sant'Angelo where he had been imprisoned by Scarpia. Angelotti's sister, the Marchesa Attavanti, has hidden a disguise for him in the church, where the painter Mario Cavaradossi is working on a painting of Mary Magdalene with the begrudging help of the Sacristan. Cavaradossi takes as his inspiration both the Marchesa, whom he has recently seen at prayer, and his beloved Floria Tosca, a prominent opera singer. Cavaradossi recognizes Angelotti and promises to help him escape, but is surprised by a visit from Tosca. Angelotti hides while Cavaradossi attempts a quick conversation with Tosca. She is instantly suspicious of Cavaradossi's cautious behavior and jealous of the woman she sees represented in his painting. Cavaradossi assuages her fears and they make plans to spend the evening together. No sooner has Tosca gone than a cannon shot signals that Angelotti's escape has been discovered. Cavaradossi and Angelotti depart immediately for Cavaradossi's villa.
The Sacristan returns with news of Napoleon's defeat by the Austrians. Arrangements have been made for an immediate Festival Te Deum and a concert at the Palazzo Farnese featuring Floria Tosca. Baron Scarpia, who has come in search of Angelotti, interrupts the preparations. Scarpia and his spies find an empty basket of food and a woman's fan bearing the Attavanti family crest. When Tosca returns to see Cavaradossi, her jealousy is again aroused by his absence. Scarpia preys on her suspicions by showing her the Marchesa's fan. When she leaves, Scarpia orders his agent Spoletta to follow her. As the congregation assembles for the Te Deum, Scarpia plans to eliminate Cavaradossi and possess Tosca for himself.
ACT II: BARON SCARPIA'S APARTMENT AT THE PALAZZO FARNESE
Scarpia relishes his plan to execute the traitors and seduce Tosca. When Cavaradossi is brought for questioning, the painter denies any knowledge of Angelotti's location. At Scarpia's request, Tosca arrives from the victory celebrations. Cavaradossi is then taken into an adjoining room and tortured. His agonized cries force Tosca to divulge Angelotti's hiding place-the well in the garden of Cavaradossi's villa. The tortures cease; Tosca and Cavaradossi are briefly reunited before Scarpia orders Spoletta to Angelotti's hiding place. As Cavaradossi denounces Tosca for her betrayal, news arrives that Napoleon has, in fact, emerged victorious over the Austrians at Marengo. Cavaradossi predicts greater and greater victory for the Republicans, and Scarpia orders him taken away for execution. When Tosca pleads for mercy, Scarpia makes his price clear: she can buy Cavaradossi's life by giving herself to Scarpia. She agrees. Since Scarpia has already ordered Cavaradossi's death, a mock execution must be arranged, and he seems to give this order to Spoletta. Tosca makes one further request: a warrant of safe passage so that she and Cavaradossi can leave the country. This done, Scarpia advances to embrace her, and she stabs him to death.
ACT III: THE ROOF OF THE CASTEL SANT'ANGELO
The song of a shepherd child and the sound of church bells signal the approaching dawn. Cavaradossi is brought into the castle yard to prepare for his death and his thoughts turn to Tosca. He is attempting to write a final letter to her when she appears. She shows him the warrant of safe passage, explains the mock execution and describes how she killed Scarpia. Tosca and Cavaradossi dream of their future happiness together. As the soldiers assemble for the execution, Tosca instructs Cavaradossi to feign death and remain motionless until she can confirm it is safe to leave. After the soldiers depart, she discovers she has been betrayed: Cavaradossi is dead. Spoletta and his men try to arrest Tosca for the murder of Scarpia, but she is too quick for them. Vowing to confront Scarpia before God, she takes her own life.
Synopsis by John Caird