Friends Jojo, Jannis, and Fabian want to earn some extra pocket money. Unfortunately, the dog Monster, whom they planned to walk, has suddenly disappeared without a trace! His owner, the supermarket manager, is completely distraught. But the three wouldn't be detectives if they didn't investigate the matter. Along the way, they have to overcome some obstacles, shadow suspects, endure a quarrel, and above all, prove their detective instincts! What role Bruno and his talking parrot play in this and why Monster ends up driving a police car will not be revealed just yet...