ACT I
Escaped political prisoner Ceaser Angelotti rushes into the church of Sant'Andrea della Valle, seeking refuge in the Attavanti family chapel.  ('Ah, finalmente!') A Sacristan enters followed by the painter Mario Cavaradossi, who is working on a portrait of Mary Magdalene.  He studies the canvas, which combines the blond haired beauty that he has seen in the church with the dark beauty of his beloved, the singer Tosca.  ('Recondita armonia') Angelotti emerges from his hiding place and is recognized by Cavaradossi, his friend and political ally.  Angelotti tells him that he has just escaped from the Castel Sant’Angelo, where he has been imprisoned by Scarpia.  Angelotti hides again when they hear Tosca outside.  ('Mario! Mario! Mario!') When Cavaradossi lets her in, she jealously asks why she heard voices in the church. Cavaradossi reassures her and they sing of their love.  When she is gone, Angelotti comes out of hiding and plots his flight with Cavaradossi.  When they hear the sound of a cannon they know that Angelotti’s escape has been discovered by the police and the two flee to Cavaradossi’s villa.  The Sacristan returns followed by clerics and choirboys.  They are interrupted by Scarpia, the chief of the secret police, who enters searching for Angelotti.  Tosca soon returns in search of Cavaradossi.  Scarpia uses a fan he has found belonging Angelotti’s sister to arouse her suspicions.  Thinking that Cavaradossi has been unfaithful, she vows vengeance and hurries off for the villa.  Hoping that she will lead him to Angelotti, Scarpia sends his men to follow her and vows to make her his. ('Tre sbirri... Una carrozza...')

ACT II
Alone in his apartment in the Palazzo Farnese, Scarpia dines and anticipates bending Tosca to his will.  ('Tosca è un buon falco!')  The spy Spoletta enters and reports that they were unable to find Angelotti at Cavaradossi’s villa and have placed Cavaradossi under arrest instead.  Cavaradossi is brought in and questioned.  Scarpia has sent for Tosca, who is in the palace performing.  She enters just as they are taking Cavaradossi away.  Upon hearing his tortured screams, Tosca reveals Angelotti’s whereabouts.  Learning of her betrayal, Cavaradossi curses Tosca’s weakness.  Tosca asks Scarpia what the price of her lover’s freedom will be and he tells her that she must submit to his embraces.  Tosca cries that she has devoted her life to art and wants to know why God would repay her with such misery. ('Vissi d’arte, vissi d’amore')  Spoletta enters with the news that Angelotti has killed himself rather than be taken prisoner. Tosca agrees to give in to Scarpia if he will set Cavaradossi free, but Scarpia tells her that he cannot pardon Cavaradossi and instead will set him free after a mock execution.  Tosca insists that he write a note of safe passage for both her and Cavaradossi.  While he is writing, Tosca notices a knife, which she takes without his notice.  After he has sealed the note, Scarpia advances on Tosca and she stabs him.  Tosca grabs the note of safe passage and quickly flees.

ACT III
Cavaradossi is brought to a platform in the Castel Sant'Angelo.  He asks for a pen and paper in order to write a letter for Tosca and reflects on his love for her.  ('E lucevan le stele') Tosca rushes in with the note of safe passage and tells Cavaradossi of Scarpia’s death.  Cavaradossi praises Tosca for her courage and Tosca explains the plan for the mock execution. ('O dolci mani') She worries whether he’ll be able to play his part and tells him that he should lie still after the gunshots until she gives him the signal.  When the firing squad comes to perform their duties, Cavaradossi falls to the ground.  She tells him that it is safe to move, but when he does not respond, Tosca realizes Scarpia’s treachery.  Having discovered Scarpia murdered, Spoletta and the others come to arrest her.  Before they can catch her, Tosca climbs on the battlement and, saying that she and Scarpia will meet before God, leaps to her death. ('O Scarpia, avanti a Dio!')