Dominique is a pretty, vivacious girl. When she witnesses a car theft, she throws herself and her bicycle under the vehicle. Jacques Mareuil, whom she then blackmails, pays her a sum to cover her debts. In reality, Mareuil, a policeman, is keeping an eye on Atcheminov, the owner of the car, but, wanting to prove that he is an unscrupulous trafficker, he comes up against Dominique's impetuosity time and again. It all ends up like in a good comedy.