In sixteenth century Greece, Gismonda, the Duchess of Athens, entertains a stream of suitors, although she only loves her little son Francesco. Prince Zaccaria, who wishes to become the duke of Athens, kidnaps Francesco and throws him into a pit holding a huge lion. The duchess, terrified that her child is in danger, offers to marry the man who rescues her boy. The deed is accomplished by a humble huntsman, Almerio, but Gismonda soon breaks her promise, not wishing to marry a commoner. To persuade him to release her from her vow, the duchess visits Almerio one night but is seen by Zaccaria and his cohort Gregoras leaving the hut in the morning. Zaccaria determines to kill the huntsman, but Gismonda stabs him at Almerio's door. Having discovered who was responsible for Francesco's entrapment, Gismonda has Gregoras arrested. Finally realizing her great love for Almerio, she bestows on him the title of duke and marries him.