In the second part of the successful children's book adaptation, Franz, Gabi and Eberhard go on a turbulent hunt for criminals during the summer holidays – and uncover a completely different secret in the process.

Franz is by far the smallest in the class, has blond ringlets and gets a high-pitched squeaky voice when he gets upset. Luckily, two best friends help: Gabi and Eberhard. When Franz discovers Hank Haberer's "10 rules for a real man" for himself one day, turbulence is inevitable and the friendship of the three gets into trouble.