Ten-year-old Annaluise, nicknamed Puenktchen, is best friends with Anton despite the difference in their backgrounds – Annaluise's parents work in the medical field and are quite well-to-do, while Anton's father is missing and his mother Elli has health problems and can only work part-time at a local cafe. When Elli's doctor advises her to take a trip to the seashore that she cannot afford, Anton steals a gold cigarette lighter from Annaluise's folks, causing serious friction between his mother and her parents.

The story covers a few days left for the students of Johann-Sigismund Gymnasium before Christmas. The main characters - students from the Tertia (Year 8) - are rehearsing a Christmas play called 'The Flying Classroom' when their attention is distracted by a brawl against the students of the local Realschule.

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 so both go off to where they have never been before. The adventure begins.