In this third film of the series of Lotte films that children know and love, the spirited girl dog Lotte gets a little sister named Roosi. Karl the raccoon and Viktor the fish are scientists who come to Gadgetville. They are taking part in a big folk song collecting competition.
Being small doesn't make life easy for little ten-year-old Victor and his friends, who not only have to face a world full of stern grown-ups but also the town bully Freddy Frogface. When a circus comes to the sleepy little town, Victor is thrilled at having the chance to perform in a talent show with his dog Sausage.