The 17-year-old twins Mieke and Mattis live in a small Bavarian town with their widowed father Jan who has a new girlfriend. One day they discover completely new feelings for each other. Mattis realizes how much he desires his sister, and Mieke, too, can hardly suppress her yearning to approach him. Nevertheless, the siblings try with all their might to fight their incestuous desire. But on a balmy summer night it happens and they climb into bed together. Once they have slept together, there is no turning back.