The embassy in Paris of the Balkan principality of Pontevedro is holding a ball. Hanna Glawari, who has inherited twenty million francs from her late husband, is to be a guest at the ball. It is known that if Madame Glawari marries a foreigner and takes her 50 millions from the Pontevedrian bank, the country will be ruined. This “secret” information has soon leaked to the high-society salons. Hanna arrives and is showered with compliments by the Parisian men hoping to get her money. Baron Zeta has selected the Petrovenian Count Danilo Danilovitsch, the First Secretary of the embassy, as the ideal bridegroom. Danilo agrees, but he does not know that the rich widow is that beautiful stranger he has recently met and who has won his heart.
The following evening, Anna hosts a real Pontevedrian garden party at her house. However her guests are more interested in money rather than in small talks, entertainment, folk songs and dances. Desiring to get money these so called “patriots” lose all sense of shame and honour, they are ready to betray their Fatherland.
Anna and Danilo are in love. They feel that their happiness is close at hand. Suddenly it seemed to Baron Zeta that he saw his wife with French attaché Camille Count de Rosillon in the summerhouse. Baron plans to compromise her and to divorce his wife and then to marry Anna to get her money.
However it is not she but Anna who left the summerhouse with Camille. To save Valencienne reputation Anna announces her engagement to Camille. A furious Danilo departs for Maxim’s, which Hanna takes as proof of his love.
Everybody meets at Maxim’s, the favorite restaurant of Count Danilo. He is asked to decode secret wire. Soon Anna and Rosillon appear. Count de Rosillon admits that he is not intended to marry Anna.
Everybody, except Danilo, asks Anna’s hand. She announces that unfortunately, by the will of her late husband, she loses all her money if she remarries. Astonished admirers refuse her. Danilo interrupts her: if she loses everything, he can now propose. And she, triumphant, explains to him that when she loses the money, it becomes the sole property of her husband. All rejoice!