Eleven-year-old outsider Stephan arrives at Castle Schreckenstein, an all-boys boarding school, where he learns about life within a community and soon finds himself being part of a funny 'pranks-competition' the boys are currently fighting against the neighboring girls of Castle Rosenfels. When the girls have no choice but to move to Schreckenstein after a failed prank, life at school is suddenly nothing like it used to be...

Schreckenstein and Rosenfels outdo each other with acts of sabotage during the competitions at Kapellsee. But shortly before the end, the competition is called off because the Count's zeppelin crashes! Count Schreckenstein manages to save himself, but now has to spend several weeks in a sanatorium - and he is financially ruined. His cousin Kuno sees selling the castle as the only solution. But the Schreckies believe they can save the school and set off in search of a forgotten treasure. They need outside help - and it comes from the girls from Rosenfels, of all people.