It's graduation day at Huntington Hills High, and you know what that means - time to party. And not just any party, either. This one will be a night to remember, as the nerds become studs, the jocks are humiliated, and freshman crushes blossom into grown-up romance.

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.