Three young men - Jacques, Pierre, and Michel - share an apartment in Paris, and have many girlfriends and parties. Once, during a party, a friend of Jacques' tells him he has a quite compromising package to deliver, and asks him if he can leave it discreetly at their place. Jacques agrees and, as he works as a steward, flies away for a one-month trip in Japan, telling Pierre and Michel about the package. Then, one of Jacques' former girlfriends drops a baby before their door, making Pierre and Michel believing it is the package they are waiting for. Their lives are then completely changed.

Victor Valance, an absent father and gambler, works with shady casino operations abroad. When he returns to Paris in need of money, he plans to take advantage that Pauline, his eldest daughter now fully responsible for the whole family, has begun to work for the Ministry of Finance. Pauline thwarts his new projects but when she realizes gangsters are looking for Victor she will put her life at risk to help him and save their family.

The cynical boss of a big insurance agency invites his top-salary employees to spend a week-end in his country house. A modest clerical worker, also invited, discovers the hidden reason for this party - and decides to take advantage of it.