Simon is new to his neighborhood. However, burglars are making the area unsafe. His home is also broken into. Since the burglars administer a sleeping drug to his dog Lotta, it becomes clear to him and his neighbor Emily that they need to take action. Of course, things turn out quite differently than they had planned. Nevertheless, the two children, with Lotta's help, ultimately manage to catch the burglars. And wait: Their classmates must also contribute to this. On the worksheets, they create masks and puppets to reenact scenes, analyze the crime scene, solve puzzles, and even learn a secret code. In the end, the criminal case is solved.