One evening, when they come home, Mr. and Mrs. Prioux are astounded to find that a certain Patrick has moved into their place. This strange young man has returned home to his parents in order to introduce his wife. The Prioux, who have never had any children, are flabbergasted, particularly as everything seems to prove that Patrick is indeed their son. Is Momo a mythomaniac? A manipulator? Have the Prioux forgotten that they had a child? Has Mrs. Prioux, who has always suffered from not having had any children, invented a son?