The film is based on a series of immensely popular Swedish children's books, about the boy Bert, who is just hitting puberty and having the usual problems with it. But that's where the usual ends abruptly.

The first appearance on screen for Bert Ljung, a normal teenager who's diary Swedes have been able to follow in well over ten books now. As in the books, he fights spots, looks for girls, runs his moped, plays with his weird friends Ake and Erik, and a lot of other stuff teenagers are supposed to do.

A feisty five-year-old girl Lotta decides to move away from home. And no, she doesn't want to put on the stupid sweater.

Lotta is a five old girl living in Sweden with her mother, father, brother and sister. She is living the very normal life of all children of her age...