The captain of a Marseille freighter suspects his wife of cheating on him with his childhood friend. The ulcerated wife decides to take a trip with her sister and this friend, and registers herself under a false name on her husband's boat. A disaster caused by the fog reveals to the household their love for each other.

A gypsy and a boatman fall in love with each other. They do not understand each other and make each other suffer. When, at last, their hearts are confounded, the young girl’s father kills the young man, thus accomplishing the implacable Bohemian law.

A woman's marriage is on the rocks ; to avenge herself, she decides to take a lover for one night .So she buys all his stock from a balloon man and flies them through the Parisian sky ; all her balloons carry a message :"I will be alone after midnight" (hence the title); a lot a suitors comme to the rendezvous : a fisherman, a soldier, a traveler , a gentleman cambrioleur (a nod to Arsène Lupin?) and others ,much to Michel, a young man in love with her's displeasure.