A widow named Blanche Montel endeavours to find a man with whom to produce a child so that she can pretend that the child was her late husband's and so inherit a fortune.

Célestin, the organist of a convent, has written and composed a light operetta under the name of Floridor. One day, the Mother Superior asks him to chaperone one of the boarders, Denise de Flavigny, who is returning home to get married. Now, Denise, for all her goody goody looks, soon proves as saucy as can be. Things get even more complicated when Célestin starts courting Corinne, the star of his operetta, to the great displeasure of a commander of dragons, the young woman's lover. Worse, the latter is none other than the Mother Superior's brother... To say nothing of Lieutenant Fernand de Champlatreux, who happens to fall in love with Denise, his fiancée that he has never seen before...!

Paris, 1830. Fleur de Marie is rescued from poverty by the mysterious Rodolphe, who is in fact the Grand Duke of Gérolstein, who has gone incognito in search of an illegitimate child he once had. Which is not at all to the taste of Sarah Mac Gregor, her current mistress who kidnaps Fleur and has her locked up in Saint-Lazare prison.