Louis Alban (Jean Rochefort) has been divorced from his wife for awhile when a ruse perpetrated by his son sends him rushing to see her, but not exactly in a direct line. After Louis reads a New Year's card from his son indicating the boy is being abused by his stepfather Bob, Louis takes off for Paris to take care of Bob. But when Louis arrives at the apartment complex where his wife and son live with the infamous Bob, he is overwhelmed by the many buildings there -- and distraught over his lack of an exact address. As he wanders around, he encounters a few others who end up about as lost as he is, including a garage mechanic and his young accountant -- both searching for a party given by the real Bob, and a militant apartment resident who lends his support and his gun to Louis' desperate search. This disparate group of people meander around the building, but in the end they fit into the carefully crafted plans of Louis' deceptive son to bring his mother and father back together.