A detective classic full of suspense and adventure - now in a new edition. Four boys and a girl are terrorized by an unknown person for weeks: they receive unusual assignments on small notes, signed by the Red U. If they fail to complete these tasks, they face betrayal, as the Red U knows that the five have been playing mean tricks on many residents of their town. The mysterious assignments become increasingly dangerous, but Boddas, Mala, Döll, Knöres, and Silli cannot figure out who is behind the enigmatic Red U. When a classmate goes missing, they once again prove their detective skills. With their help, the boy can be rescued, and the mystery of the Red U can finally be solved.