Teenagers Sharon McKendrick and Susan Evers (Hayley Mills) meet at Miss Inch's Summer Camp for Girls. Their alike appearance initially causes resentment and a rivalry in which they continually pull pranks on each other, ultimately disrupting a dance with a neighboring boys camp. As punishment, they must room together in the isolated "Serendipity" cabin and have all meals at the "Isolation Table" for the remainder of the camp season. They eventually overcome their mutual dislike, then discover they are identical twin sisters. Their parents, Mitchell "Mitch" Evers (Brian Keith) and Margaret "Maggie" McKendrick (Maureen O'Hara), divorced shortly after their birth, splitting physical custody between them. Eager to meet the parent they never knew, the twins decide to switch places by having the same haircut and undergoing a crash-course on each other's life.