What is the last name of the painter Scarpia mistrusts and believes complicit in Angelotti's escape?
Inside the church of Sant'Andrea della Valle
Cesare Angelotti, former consul of the Roman Republic and now an escaped political prisoner, runs into the church and hides in the Attavanti private chapel – his sister, the Marchesa Attavanti, has left a key to the chapel hidden at the feet of the statue of the Madonna. The elderly Sacristan enters and begins cleaning. The Sacristan kneels in prayer as the Angelus sounds.
The painter Mario Cavaradossi arrives to continue work on his picture of Mary Magdalene. The Sacristan identifies a likeness between the portrait and a blonde-haired woman who has been visiting the church recently (unknown to him, it is Angelotti's sister the Marchesa). Cavaradossi describes the "hidden harmony" ("Recondita armonia") in the contrast between the blonde beauty of his painting and his dark-haired lover, the singer Floria Tosca. The Sacristan mumbles his disapproval before leaving.
Angelotti emerges and tells Cavaradossi, an old friend who has republican sympathies, that he is being pursued by the Chief of Police, Baron Scarpia. Cavaradossi promises to assist him after nightfall. Tosca's voice is heard, calling to Cavaradossi. Cavaradossi gives Angelotti his basket of food and Angelotti hurriedly returns to his hiding place.
Tosca enters and suspiciously asks Cavaradossi what he has been doing – she thinks that he has been talking to another woman. Cavaradossi reassures her and Tosca tries to persuade him to take her to his villa that evening: "Non la sospiri, la nostra casetta" ("Do you not long for our little cottage"). She then expresses jealousy over the woman in the painting, whom she recognises as the Marchesa Attavanti. Cavaradossi explains the likeness; he has merely observed the Marchesa at prayer in the church. He reassures Tosca of his fidelity and asks her what eyes could be more beautiful than her own: "Qual'occhio al mondo" ("What eyes in the world").
After Tosca has left, Angelotti reappears and discusses with the painter his plan to flee disguised as a woman, using clothes left in the chapel by his sister. Cavaradossi gives Angelotti a key to his villa, suggesting that he hide in a disused well in the garden.  The sound of a cannon signals that Angelotti's escape has been discovered. He and Cavaradossi hasten out of the church.
The Sacristan re-enters with choristers, celebrating the news that Napoleon has apparently been defeated at Marengo. The celebrations cease abruptly with the entry of Scarpia, his henchman Spoletta and several police agents. They have heard that Angelotti has sought refuge in the church. Scarpia orders a search, and the empty food basket and a fan bearing the Attavanti coat of arms are found in the chapel. Scarpia questions the Sacristan, and his suspicions are aroused further when he learns that Cavaradossi has been in the church; Scarpia mistrusts the painter, and believes him complicit in Angelotti's escape.
Cavaradossi