The church of Sant’Andrea della Valle
Angelotti, an escaped political prisoner, seeks refuge in a family chapel – his sister, the Marchesa Attavanti, has left him the key. The sacristan enters, muttering about the mess the painter Mario Cavaradossi is making. The artist soon arrives, and the sacristan observes how much the Magdalene in his painting resembles a young woman (the Marchesa) who has been visiting the chapel as of late. Cavaradossi admits that he has used her as a model, and muses over how her blue eyes compare to the dark ones of his lover, the opera singer Floria Tosca.
Left alone, Cavaradossi discovers Angelotti hiding and recognizes his good friend. They are interrupted by the voice of Tosca, and Angelotti takes cover once again. When the diva finally enters, it is clear she is prone to jealousy – she heard voices and suspects a rival. Cavaradossi reassures her, and they make a date later that evening at a secret villa. Suddenly, Tosca recognizes the visage in the painting as the Marchesa Attavanti and her suspicions are renewed. The artist again pledges his heart and agrees to paint the eyes dark to match those of his lover. Tosca leaves satisfied.
Angelotti reemerges and Cavaradossi agrees to help him escape. He knows a private route to the villa, and the Marchesa has provided woman’s clothing as a disguise. The two men leave in haste. The sacristan reenters with news of Napoleon’s defeat at Marengo. He assembles the choir to sing a Te Deum in thanksgiving.
The chief of police, Scarpia, appears and interrogates the sacristan about the escaped prisoner. He observes the unlocked chapel and finds evidence of Angelotti’s visit – Cavaradossi’s empty lunch basket and the fan of the Attavanti, part of the disguise but carelessly left behind. The painter immediately becomes suspect. When Tosca returns to tell Cavaradossi that she is no longer free that evening, as she must sing in the celebratory cantata at the Farnese palace, Scarpia decides to use her jealousy to his advantage. He shows her the fan, and Tosca again becomes agitated. As she hurriedly departs, police agents follow in quick pursuit.
As the choir begins the Te Deum, Scarpia savors his plan – Tosca’s lover shall be sent to the gallows, while he shall have his way with her.
The Farnese Palace
At his headquarters, Scarpia muses over his next moves. The criminals shall soon be in his custody, and he has sent word for Tosca to meet with him after singing the cantata. Spoletta soon informs him that Cavaradossi is in custody, but Angelotti is nowhere to be found. Scarpia interrogates the painter, who remains obstinate to his questions. Tosca arrives presently, and Cavaradossi is led into the next room.
Following her lover’s instructions, Tosca first admits to know nothing of Angelotti’s whereabouts. But as Cavaradossi’s torture begins, his moans weaken her resolve, and she soon reveals that the escaped convict is hiding in the well at the villa. Cavaradossi is again brought into the room and curses Tosca’s weak resolve. Suddenly, Sciarrone enters with news that Napoleon was in fact victorious at Marengo, invigorating the republican Cavaradossi, to the annoyance of Scarpia. The painter may gloat only a short while, for the hangman’s noose awaits him at dawn.
Tosca begs Scarpia to spare her lover, and Scarpia strikes a cruel bargain – he will be released only if she will submit to one night of passion. After some hesitation, Tosca tearfully agrees to the plan and demands Cavaradossi be freed at once. Scarpia counters that the painter must be believed to be dead and a mock execution “in the manner of Count Palmieri,” he instructs Spoletta, must take place. As he writes out a safe conduct pass, Tosca spies a knife on the dinner table. When Scarpia goes to embrace her, she stabs him to death.
The platform of the Castel Sant’Angelo
Just before dawn breaks, Cavaradossi prepares for his execution. He bribes the jailer with his ring to deliver a message to Tosca. As he begins to write, he wistfully recalls their love affair. Moments later, she appears and after showing him the safe conduct pass, confesses her evil deed. She then details the plan for the mock firing squad – he must fall when he hears the shots and remain lifeless until after the soldiers have left.
As the execution takes place, Tosca watches from nearby and compliments Cavaradossi on his acting ability. But she soon learns Scarpia has had the last laugh – the bullets were real and Cavaradossi is dead. Surrounded by Scarpia’s henchmen, Tosca climbs to the highest rampart and jumps to her death.