Percival and Nellie go to New York so that Percival can run the family business now that his father has died. Mrs. Oleson gets very depressed because of Nellie leaving. The Olesons decide to adopt a girl to take the place of Nellie. While they are in Sleepy Eye, they find a girl that looks almost exactly like Nellie when she was young.

Nancy turns out to be worse than Nellie ever was. She even locks another girl in the ice house. The students devise a plan to teach Nancy a lesson. They trick her into being the star in a dunking tank. Also during this episode, Adam and Mary move to New York so that they can earn a living and Hester Sue comes to Walnut Grove to work at the restaurant.