Act I. The Church of Sant’Andrea della Valle.

Angelotti searches for the key and hides in the Attavanti Chapel. The Sacristan brings clean brushes, and the painter, Mario Cavaradossi, arrives shortly thereafter. The Sacristan points out that Cavaradossi hasn’t eaten. Cavaradossi climbs the scaffold and examines his portrait of Mary Magdalen, depicted as blonde with blue eyes. In it the Sacristan recognizes a woman who comes daily to pray. Cavaradossi admits that, unknown to her, this visitor was his model. He compares her light features to the darker hair and black eyes of the singer Floria Tosca, who is the woman he loves.

As the Sacristan leaves, he tells Cavaradossi to lock the door. Angelotti, thinking the church empty, emerges and is overjoyed to see his friend Cavaradossi. He explains that he has just escaped from the Castel Sant’Angelo. Suddenly, they hear a woman’s voice calling, “Mario!” Cavaradossi tells Angelotti to hide—it is Tosca, and she is quick to be jealous. He gives Angelotti food and hurries him off.

When he lets Tosca in, she believes he is hiding a mistress—she heard voices—but he placates her. Tosca reminds him that she is singing a concert later. She wants him to wait for her when it’s over so they can go together to his villa. Cavaradossi happily agrees to her plan but tells her that now she must leave because she is disturbing his work. Recognizing the face of the Marchesa Attavanti in the portrait, Tosca is furiously jealous. He soothes her, saying he loves only her.

When she leaves, Cavaradossi tells Angelotti that it is better if Tosca knows nothing. Angelotti reveals that his sister, the Marchesa Attavanti, is helping him escape from Scarpia, the police chief, by leaving him a disguise by the altar—some women’s clothing. He plans to depart once it is dark. Cavaradossi, who hates the hypocritical Scarpia, offers Angelotti the use of his villa, accessible through hidden ways from the church garden, where he can hide in a secret chamber. Suddenly, they hear a cannon signaling Angelotti’s escape. Cavaradossi decides to leave with Angelotti.

The Sacristan comes to crow to Cavaradossi about a defeat suffered by Napoleon Bonaparte. He is surprised not to find the painter, and he gathers the choristers to tell them the news. Scarpia arrives, having tracked Angelotti to the church. Examining the Attavanti Chapel, the Sacristan discovers Cavaradossi’s empty lunch basket. Meanwhile, Scarpia has found a fan belonging to the Marchesa Attavanti.

Tosca comes back to tell Cavaradossi that their quiet evening will have to wait: She must attend a celebration. Scarpia shows her the fan, saying that the painter and the Marchesa were interrupted and left so quickly that the lady dropped her fan. Scarpia is delighted to see Tosca’s jealousy rise. He signals to his henchman Spoletta that Tosca is to be surreptitiously followed.

As the church fills for a service Scarpia gloats that he has unleashed Tosca as a falcon after prey. He seeks two ends: Cavaradossi’s death and Tosca’s submission to his desires.

Act II. The Palazzo Farnese

Scarpia sits in his apartments later that night. He can hear from the orchestral music playing downstairs that Tosca hasn’t arrived yet. He sends a policeman, Sciarrone, to wait with a note for Tosca requesting her to come when her performance is over. He eagerly anticipates his conquest of her, planning to use her love for Cavaradossi to entrap her.

Spoletta reports that his men followed Tosca to a villa. She didn’t stay long. When she left, they ransacked it without finding Angelotti. Spoletta was sure from Cavaradossi’s attitude that he knew something, so he arrested him and brought him in.

The sounds of a cantata signal Tosca’s arrival. Scarpia sends for Cavaradossi and questions him about Angelotti’s escape, but Cavaradossi says he knows nothing about it. When Tosca arrives, Cavaradossi is led to the next room to be tortured. Scarpia offers Tosca a seat.

Scarpia describes to Tosca what is happening. Although in great pain, Cavaradossi reveals nothing. Tosca quickly becomes hysterical and begs Cavaradossi to let her tell Scarpia what he wants to know. When she reveals Angelotti’s hiding place Scarpia ends the torture. Cavaradossi, who has fainted, is brought back in. He is horrified to learn that Tosca has betrayed Angelotti.

Sciarrone bursts in with news of Napoleon’s victory at Marengo, a blow to Scarpia but great news for Cavaradossi. Scarpia sentences Cavaradossi to death. The policemen lead him away.

Scarpia hints that Tosca can save Cavaradossi. She asks his price and finds out that it is not money he wants from her. Scarpia finds her hatred appealing. She is free to go, he says, but then Cavaradossi won’t live long enough to be pardoned. Tosca, trapped, asks God why her faith is being rewarded this way.

Spoletta soon reports that Angelotti has killed himself. Tosca decides to submit to Scarpia if he will save Cavaradossi. Scarpia says he can’t let it be known that he has pardoned a prisoner, so they’ll have to fake an execution. He orders Spoletta to set up a firing squad at daybreak, the way they did it for Palmieri. Spoletta indicates he understands.

After Spoletta leaves, Tosca asks for safe conduct out of Rome. As Scarpia prepares a pass, she notices a knife. Scarpia approaches her to collect his reward. Tosca stabs him. After he dies, she wipes the blood from her hands, then collects the safe conduct.

Act III. The Castel Sant’Angelo

In the distance, a shepherd sings. A jailer receives Cavaradossi, informing him he has an hour to live. Cavaradossi refuses a priest but offers his ring if he can write a letter. Starting to write, he is overcome by love for Tosca and sadness at leaving life when he has so much to live for.

Spoletta escorts Tosca in. She shows Cavaradossi her safe conduct—for her and a man traveling with her—and explains how she got it. Cavaradossi is astonished. She has arranged their escape. All he must do is fall convincingly when the firing squad shoots, their guns loaded with blanks. She anxiously watches the execution, worried that Cavaradossi will move before the firing squad leaves. Finally, she goes to him, telling him it’s time to go. When he doesn’t move she realizes he is dead.

Suddenly she hears voices. Sciarrone has discovered Scarpia. Before the police can capture her, she leaps from the parapet.