Hanni and Nanni are not only sisters, but also best friends. The twins are inseparable and always up to something. When they cause a wild chase through a department store, their wealthy parents have had it: They send the girls to the posh boarding school Lindenhof in order to teach them some manners. While sweet-tempered Nanni quickly makes new friends, the impulsive Hanni has a hard time accustoming herself.

The summer break is over and the twins returned to Lindenhof. That has now changed a lot. Because Mrs Theobald had to travel, Mademoiselle Bertoux has taken the lead.

The Lindenhof School is expecting a busload of proper young English ladies as exchange students. The shock is great when the students turn out to be teenage boys! But while Mademoiselle Bertoux is delighted to stage “Romeo and Juliet” with real boys, both Hanni and her sister Nanni fall for their “Romeo,” Clyde.

After plotting a way to get kicked out of boarding school, the twins diverge for the first time in their lives when Nanni starts enjoying her stay.