Jackson and Helen are in love and about to have their first child when they move in with Jackson's mother, Martha, in order to take care of the family estate. But all is not well in this household. Martha is jealous of her son's affection for Helen, and, despite her Southern smile, she's starting to act strangely. As Helen tries to create a happy home life, Martha attempts to divide the family so that Jackson will become hers alone.

Before going on vacation, self-involved psychiatrist Dr. Leo Marvin has the misfortune of taking on a new patient: Bob Wiley. An exemplar of neediness and a compendium of phobias, Bob follows Marvin to his family's country house. Dr. Marvin tries to get him to leave; the trouble is, everyone loves Bob. As his oblivious patient makes himself at home, Dr. Marvin loses his professional composure and, before long, may be ready for the loony bin himself.