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.

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.