The residents of the apartment building on Rue Montmartre are a motley crew of oddballs and eccentrics. The daring son of a professor couple is in love with a sexy student who supplements her pocket money by working as an au pair. And then there's Monsieur Calomel, the crazy but helpful neighbor who's always ready with a funny face...

Robert Langlois is now married to Catherine, the former housemaid. And they would live happily ever after if the housing crisis did not force them to live together with Gabrielle and Fernand, Robert's parents. For, despite the good will on either side, tension soon arises. What else to expect when there is too little space in their Montmartre apartment for four people (then for six then eight, the couple having... two pairs of twins!) ; the continued presence there of Fernand (who loves peace and quiet) after he is driven to retirement ; the difficult beginnings of Robert as a lawyer in a room of the apartment, etc... Other troubles follow and the harried family is on the verge of implosion...