Maria lives with her grandfather in a secluded fishing hut on Lake Constance where they barely survive on what the fishing grounds provide. The daughters from next door make things worse by scaring away the fish with their motorboat. But Hans, the son of a rich family, falls in love with Maria and tries to help her, although she is unsure if he can be trusted.
Two nine-year-old girls—rude Luise Palfy and respectful shy Lotte Körner—meet on a summer camp. Apart from their different hair-do, they look alike. They have never seen each other before, but soon find out that they are identical twins. It turns out that their parents divorced, each keeping one of the girls. They decide to trade places at the end of the summer. Lottie curls her hair, Lisa braids hers, and both go off to where they have never been before. The adventure begins.
