ACT I In the Church of Sant’ Andrea della Valle an escaped political prisoner, Cesare Angelotti, takes refuge in the family chapel where his sister, the Marchesa Attavanti, has left women’s clothing for his disguise. When the painter Mario Cavaradossi arrives to continue work on his canvas, Angelotti recognizes him as a fellow sympathizer and asks for his help. Cavaradossi enthusiastically agrees, gives him food and urges him back into the chapel as his lover, the beautiful and tempestuous opera singer Floria Tosca, is heard outside. She jealously questions Cavaradossi and reminds him of their rendezvous that evening. Recognizing the likeness of the Marchesa Attavanti in her lover’s painting her suspicions are aroused, but he reassures her and she leaves. A canon shot signals the discovery of Angelotti’s escape and the two men flee to Cavaradossi’s villa.Baron Scarpia, chief of secret police, arrives in search of Angelotti. When Tosca returns looking for Cavaradossi Scarpia shows her a fan he has found. It bears the Attavanti crest and her suspicions are renewed. Thinking Cavarodossi faithless, Tosca tearfully vows vengeance and leaves the church. Scarpia sends his agents to follow her.   ACT II Back in his apartments in the Farnese Palace, Scarpia relishes the thought of having Tosca within his grasp. The agent Spoletta arrives having failed to find Angelotti. He has, however, arrested Cavaradossi who is brought in and interrogated while Tosca is heard singing at the Royal Gala downstairs. Summoned by Scarpia, she arrives just as her lover is led away to be tortured. Completely distraught at the sound of her lover’s suffering, she reveals Angelotti’s hiding place. Cavaradossi is carried in and, realising what she has done, he denounces her angrily. At that moment a messenger arrives announcing that Napoleon has won the battle of Marengo, a defeat for Scarpia’s side. Cavaradossi, jubilant and defiant, is dragged out to await execution. Tosca, alone with Scarpia, agrees to yield to him in exchange for the life of her lover. Spoletta interrupts with the news that Angelotti has killed himself. The Baron pretends to order a mock execution for Cavaradossi and Spoletta leaves. At the insistence of Tosca, Scarpia writes a safe conduct for the lovers. As he attempts to embrace her Tosca fatally stabs him and makes her escape.   ACT III At dawn, on the ramparts of the Castel Sant’Angel, Cavaradossi prepares for his execution. Having bribed the jailer to deliver a farewell note to Tosca he is overcome with despair as he attempts to write. Suddenly Tosca arrives with the safe conduct and the story of her encounter with Scarpia. She tells Cavaradossi of the mock execution and the firing squad arrives to carry it out. The soldiers fire and depart and Tosca discovers the treachery of Scarpia - the bullets were real. Spoletta, having discovered Scarpia’s corpse, arrives with other agents to arrest her. Tosca, in a final act of defiance, flings herself from the parapet to her death.