Young Kuttel belongs to a group of working-class children who live in Berlin at the beginning of the 1930s. In the big summer holidays in 1931, the children want to make a race with their model boats and choose as a venue for the small artificial water in the park of their neighborhood. All children in the area are invited to participate in the competition. But there is a traitor among them, who tells the company to the local police officers, who in any case look with arrogance on the "Reds"...