The Mupfer gang is again forced to admit defeat by the Schmutzer gang, and the Mupfers then begin to stir up trouble. If the bosses - Meier and Ferri - do not come up with a brillant idea soon, they will be toppled. Ivonka Pivonka, a 12-year-old girl who is inclined to snoop, is on the trail of three robbers of postal money transports. Unfortunately, Ivonka is more curious than she is careful. After being caught, she is locked up at gentle-natured Kitty's apartment. Meier and Ferri read about Ivonka's disappearance and decide to help her escape. With the help of Liese, Ivonka's best friend, and Alice and Aline, two elderly ladies, they begin to track down the postal robbers.