Thomas, the father of 12-year-old Paul, has disappeared without a trace for a year now. When the boy and his best friend Max spend the summer holidays on the Swabian Alb, the two try to investigate the disappearance of Paul's father. To do this, they want to find a legendary cave that Thomas studied. But his notes have to be deciphered first. They also have to deal with wild animals and an almost impenetrable labyrinth in the mountain forests.