Le pain de ménage

Two married couples share the same holiday house. Everything seems to go smoothly except that Pierre, one of the two husbands, is irresistibly attracted to Marthe, his friend's wife. As for the latter, she feels exactly the same for him. One night (or is it the same thing every night?) Pierre and Marthe remain in the living room after their mutual partners have gone to bed. They talk and banter pleasantly until they half-wordily evoke the present that could be theirs if they had married each other or what future they could contemplate if they escaped together.