Un fil à la patte: Bois d'Enghien, engaged to a young girl from a good family, has to break up with Lucette Gautier, his mistress, a dilettante of salons. Not having been able to tell her of his break-up, he finds her at her fiancée's house, invited for the event. A Mexican general, jealous of his rivals, arrives and complicates the situation, as does a notary clerk, Bouzin, a singer in his spare time.