Matthias is new in class and not very popular. He does not take school serious and gets bad grades. The other boys want to know the reason for his attitude and challenge him to a test of courage. Matthias is supposed to sit down with them in a cold room for as long as possible. When Matthias still keeps mum about himself, the boys lock him up in the cold room. Being the only one who feels remorse, Heiner frees Matthias from the cellar. Heiner knows about Matthias′ problems, since he is responsible for the death of Matthias′ mother′s guide dog, which is the reason why Matthias has to accompany his mother on daily errands. To atone for this guilt, the classmates unanimously decide that Heiner′s dog Rüpel shall be turned into a guide dog for Matthias′ mother.