The wealthy editor Pierre Brochant and his friends have a competition: every Wednesday, each one of them invites the dumbest jackass he can find for a dinner, where each one of the guests is invited to talk about himself as much as possible. Later, after the guests say goodbye, the group of friends makes fun and elects the more stupid and imbecile guest. Pierre invites François Pignon, a man that works in the Internal Revenue Service (IRS) and makes "maquettes" to forget his beloved wife, who had went away with a friend of him two years ago, for the dinner. However, a tough pain in one vertebra of his spinal column does not allow Pierre to meet his friends for the game and he stays alone with solicitous, but clumsy and stupid François in his apartment. Every attempt of François helping Pierre goes wrong, becoming the night of Pierre a terrible nightmare.