Count Lodovico is banished from Rome for debauchery and murder; his friends, Gasparo and Antonelli promise to work for the repeal of his sentence. The Duke of Brachiano has conceived a violent passion for Vittoria Corombona, daughter of a noble but impoverished Venetian family, despite the fact they are both married to other people. Vittoria's brother Flamineo, employed as a secretary to Brachiano, has been scheming to bring his sister and the Duke together in the hope of advancing his career, much to the dismay of their mother, Cornelia. The plan is foiled by the arrival of Brachiano's wife Isabella, escorted by her brother and Cardinal Monticelso. They are both outraged by the rumours of Brachiano's infidelity and set out to make the affair public; before that happens Brachiano and Flamineo arrange to have Camillo (Vittoria's husband) and Isabella murdered.