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...!