Mr. Belvedere encounters an insufferable girl named Brenda (Emily Schulman) while waiting in line at a fast food restaurant, and Mr. Belvedere soon realizes that her family needs him just as much as the Owens family does. Soon, the Owens family begins to see less and less of Mr. Belvedere and they discover that he has been moonlighting for the other family. It soon turns out to be an all out war between families over who gets to keep Mr. Belvedere.