 Paris, 1830. Valentin (Jean Dujardin) loses himself in alcohol, gambling and women. He does not believe in life and especially not in love. His uncle Van Buck (Gerard Jugnot) believes only in the virtues of money and trade. Everything separates them until the day when Van Buck, to improve his public image, wants to make Valentin marry the young and impoverished Baroness Cécile(Melanie Doutey). Valentin, who has absolutely no desire to get married, bets that he can easily seduce her in 24 hours and thus prove that she, like all the others, is not worth loving... But Cécile, who believes in true love, will prove much more difficult to woo than envisaged and Valentin will have to use all possible stratagems to try and win his bet. The game of cat and mouse starts... But who is the cat?