A series of stupid coincidences causes the young Munich painter Paul to convert his uncle's castle into a hotel for four weeks. But he can't complain: business is good and he has plenty of guests. For exmple, there's Theo Muller with his revue troupe. For reasons of "sound", Muller calls himself "Miller", which, of course, causes more confusion. His daughter, the beautiful Evelyn, is confused with Mabel Miller, who has come to the hotel on a mission for her filthy rich father ... namely, to estimate the worth of the castle.

A new teacher, Dr. Dr. Bach, is transferred from his quiet village elementary school to the Mommsen Gymnasium, bringing along his nephew Jan. Bach's lackadaisical methods raise the suspicions of the other teachers.

Pepe Nietnagel and his fellow students of the Mommsen school come up with all kinds of ideas to get out of doing any actual school work. This includes simulating suicides, setting off the air-raid sirens and abusing the school director's new broadcasting system. They succeed in sending their teacher to a sanatorium and get a replacement that turns out to not be so bad after all.

Pepe Notnagel (who inexplicably had his name changed from the first movie's Nietnagel) and his classmates scheme to get around doing any actual school work by cheating or sending their teachers to the sanatorium. A Swiss documentary film maker disguises himself as his brother in law, who got a position as an exchange teacher, to aid his project of making a movie about the current youth.

Mommsen Gymnasium director Taft secretly places his nephew as a spy with the difficult class of Pepe Nietnagel. During the celebration for the 100th anniversary, a simulated fire forces the school to shut down for a week. The director's attempt to get a tough teacher assigned by the department of education results in the exact opposite because of Nietnagel's intervention.

Due to a plot by the teaching staff, headmaster Taft is forced into early retirement and Knörz is appointed headmaster. However, they didn't count on class 13a, and especially not on their spokesperson Pepe Nietnagel. They are anything but happy about losing Taft, their favorite enemy. Without further ado, Pepe and his friends join forces with Taft and hatch a series of daring pranks to get back at Knörz.

Pepe Nietnagel's father has a valuable stamp collection stolen in Amsterdam. Street musician Pit recovers it. To show his gratitude, Pit is invited to Baden Baden and enters the Mommsen Gymnasium. There, he joins Pepe in his pranks.

The down-and-out private detectives Rudi and Moritz join Karin and Gerda on the hunt for an inheritance million. According to the testator's will - Aunt Trude from Buxtehude - the money must be received by Gerda within a week.

Beautiful Vienna during the Austro-Hungarian era. Lixie, a court councilor's daughter raised in a middle-class family, has fallen in love with the piano teacher Toni. To make a good impression on Lixie's strict father, Toni urgently needs a job. Then chance comes to Lixie's aid. At the Hotel Sacher, she meets Archduke Peter Ferdinand, the very man who could help Toni. But the Archduke only has eyes for Lixie. An unsuitable love affair develops between the two, which quickly escalates into a political scandal in Vienna's high society.