Marc Thiriez, a middle aged Parisian, asks his wife if he should shave off the moustache he has sported for most of his adult life.

His wife, Agnès, wryly comments that she wouldn't recognize him without it, yet as she leaves, Marc shaves the moustache off.

Serge tells a story about Agnès: during their relationship, she was sneaky but refused to admit her guilt even when everyone was certain she was at fault.

Frustrated that Serge and Nadia also do not notice his shaven moustache, Marc fights with Agnès in the car as they return home, frightening her.

As they lie in bed that night, another fight ensues as Agnès tells Marc he's never had a moustache and that she fears for his sanity.

Marc finds a photo album of pictures from their holiday in Bali, all of which show him sporting his moustache.

Marc grows more paranoid and confused when even his co-workers don't acknowledge that he has shaven his moustache.

Agnès' friend Bruno calls and Marc tells him to stop kidding him about his moustache.

Marc arrives back at the hotel one day to find Agnès awaiting him, as though she has been with him the entire trip, to his shock and confusion.

Agnès makes fun of his brightly patterned "clown" jacket and asks him why he bought it, hoping he will not wear it in Paris.

Many critics have said that the film's events are not literal, but metaphorical and are symbolic of Marc's loss of identity (or of a possible mid-life crisis).