The entire Nelson family become embroiled in confusion by the misunderstandings caused when Ozzie invites the attractive grown-up sister of a school chum to stay with the family during a centennial celebration in the community of Hillsdale. Meanwhile, Harriet unknowingly duplicates Ozzie's hospitality by extending an invitation to male guest. The tranquility of the Nelson home is shattered when Ozie and Harriet are pitted against one another in a game of tolerance while trying to keep their emotions at bay. Meanwhile, Ricky is kidnapped at the Fair by a pair of hoodlums, who have come to rob the Fair office.