The first part of the popular "Lümmel" comedies about student pranks and teachers in trouble. At the venerable Mommsen-Gymnasium, Pepe Nietnagel and his classmates take it out on their teacher Knörz. Apparently, Knörz is planning to fail as many students in their final exam as possible. But Pepe and his friends take action. their crazy pranks push old Knörz to the verge of madness. Thus, Knörz has to retreat to a sanatorium. His successor, Dr. Kersten, is highly respected by the students. But when Dr. Kersten falls in love with the daughter of the director, Pepe has new work on his hands.