Bert is finally turning 13. After years of waiting, he is finally becoming a teenager. For his birthday, he wants Rebecka from the parallel class, wrapped in shiny foil or jumping out of a cake. The worst thing that can happen in life is a health check, especially if you are 13 years old. Bert, Åke, Klimpen, Torleif, and the other boys in the class sit petrified with fear, waiting for the extremely terrifying Sister Ilse. The class is raising money for a class trip. Bert comes up with an idea—they will organize a gala where Bert's rock band, Heman Hunters, will play. At the same time, Klimpen threatens to perform as a stand-up comedian. Bert's new love is called Nadja Nilsson. Through Torleif, he finds out that she plays the violin, which Bert immediately starts practicing instead of soccer. But what will he become? A violin-playing phantom in love or a celebrated goal scorer?