Setting: Pontevedrian Embassy in Paris, France, 1905.

Baron Zeta is hosting a party at the Pontevedrian embassy.  One of the guests, Hanna Glawari, is visiting Paris after the death of her husband.  Zeta must prevent her from marrying a foreigner. If her late husband’s wealth is taken out of Pontevedro, it would bankrupt the country.  At the party she meets Count Danilovich. They had once wished to marry when she was poor, but were prevented by his uncle.  He now scorns her money and pretends not to care about her.  Zeta urges Danilo to marry Hanna to keep her money in Pontevedro.  Another guest is Camille de Rosillon who is engaged in a mild flirtation with Baron Zeta’s wife, Valencienne.  She reminds Camille of her respectability and warns against becoming too serious.

Hanna hosts a garden party the next day. Danilo attends but remains aloof.  Camille and Valencienne agree to end their flirtation but meet one last time in the garden summerhouse.   Valencienne tells Camille he should marry Hanna.  Zeta also plans to meet in the summerhouse with Danilo and his aide.  All arrive simultaneously but Hanna is able to take Valencienne’s place before she is seen by Zeta. Camille declares his love for Hanna.  Hearing this makes Danilo jealous.  Hanna, who is enjoying the farce, announces she will marry Camille.

Danilo forbids Hanna’s marriage out of patriotic duty and but then learns that the planned marriage was just a jest.  He admits his love for her and accepts her wealth gracefully.  Zeta forgives his wife and all join in a salute to women and their unpredictable ways.