Teenager Petr doesn't get on very well with his strict father, and when his father sells his beloved female dog Irina, he feels very much alone. He therefore easily falls under the influence of the older boy Panter, who is making money from fraud and theft. He gets Petr and young Fenek involved in his nefarious activities. One day Fenek throws a cartridge under a tram and the explosion causes nasty injuries to a young girl. Petr is present at the explosion and in fact it is he that the people around the tram notice, because he is wearing a white sweater.