On an otherwise normal day, Étienne, a happily married man and a good father, sees something that stops him dead in his tracks: a gorgeous woman in a billowing red dress. Long after she has left his vision, her memory continues to haunt his mind. He falls instantly in love with her and tries everything to get to know her better. Helping Étienne snare his elusive lady in red are his three bumbling buddies, which all have secret affairs and/or cheat on their wives.

Having fortuitously discovered a photograph in which Marthe embraces someone unknown, Étienne Dorsay becomes jealous and imagines various stratagems to identify the lover. In the meantime, he and his friends acquire a weekend house for a very low price.