When new student Melanie (Lorna zu Solms) turns up at the Otto Leonhard high school, Felix’s (Oskar Keymer) world is turned upside down. Much to the suspicion of Ella (Lina Hüesker) and Felix’s gang. They believe that Melanie is behind a series of thefts which only began when she started school. On a class trip things come rapidly to a head, if only because Felix had learned the secret art of shrinking from school ghost Otto Leonhard (Otto). So when Felix’s friends nearly mess up his date with Melanie, he impulsively shrinks them to a tenth of their size. And suddenly nothing goes according to plan any more.
In the third part of this well-known family entertainment series, the central characters again have to defend their school, only this time adventure sends them on a quite extraordinary class trip. Great fun for the whole family.