Lothar, Olaf, Bob and the other pioneers have the task of looking after the castle above the town. However, they mainly get up to mischief, which is why the town fathers take the job away from them again and even exclude them from the upcoming 800th anniversary celebrations. The boys hold a council on how to recapture the castle. Legend has it that the Hussites from Bohemia once stormed the castle and they, who see themselves as their descendants, want to do the same. Olaf is in favor of the violent way, but Lothar and Bob are not. They convince the others that good work is the better way, repair the castle ramparts and dig everywhere to find the hitherto missing proof of the truth of the legend, the presence of the Hussites. They actually succeed. They are restored to their former rights and are of course allowed to take part in the celebrations.