Mr. Wilson’s ever-present annoyance comes in the form of one mischievous kid named Dennis. But he’ll need Dennis’s tricks to uncover a collection of gold coins that go missing when a shady drifter named Switchblade Sam comes to town.

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.