Floria Tosca, a famous Italian opera singer, suspects that her lover, Mario Cavaradossi, is unfaithful and secretly follows him to his villa on the outskirts of Rome. La Tosca is relieved to discover that Mario is harboring not another woman but Cesare Angelotti, a political prisoner. Her relief turns to despair, however, when Baron Scarpia, Rome's tyrannical chief of police, arrives and demands that Mario turn Cesare over to the authorities under penalty of torture.