Sharon and Susan are initially able to carry off the ruse, but in California, their plan hits a snag when Mitch introduces his daughter to a young woman named Vicky Robinson (Joanna Barnes), Vicky, who aspires to be the second Mrs. The two parents would ultimately have to "un-switch" them, when the girls hope their parents will fall in love all over again. The other thing they believe is that their parents still love each other, why else had neither ever remarried. Wanting to get to know and ultimately love the parent they never met, Sharon and Susan decide to switch places, Sharon will go to California and pretend to be Susan, and Susan will go to Boston and pretend to be Sharon. It is during this confinement that they finally get a chance to know each other and learn that they are indeed twins, separated when they were babies when their parents, Maggie McKendrick (Maureen O'Hara) and Mitch Evers (Brian Keith), divorced. After the girls carry out one battle after another against each other, the camp administrators ultimately place the two in solitary confinement, the two eating, sleeping, and playing only with each other. It's hate at first sight, as besides the differing length of their hair, they look exactly the same. Thirteen-year-olds prim and proper Bostonian Sharon McKendrick (Hayley Mills) and tomboyish Californian Susan Evers (Hayley Mills) meet at summer camp.