As described in a film magazine, determined that her son Francesco (Verdi) will have every advantage of a successful reign when he grows to manhood, Duchess Gismonda refuses all offers of marriage. A sudden danger to her son prompts her to offer her kingdom to the man who rescues the child. Almerio (Foote) braves the dangers of the lion's den to save the child, but because he is a slave the Duchess refuses to fulfill her vow. Gradually, she learns to love him, and after he assumes the guilt for a murder that she committed, Gismonda confesses to the crime and in the presence of her people makes Almerio her consort.