A novel for 7-9-year-old children, which has become a permanent part of the canon of school reading. Its heroine is Kasia - an exemplary student and a favorite of her parents and grandparents - whose little sister is born. The jealous girl experiences a rebellion that leads to self-destruction: she becomes aggressive, gets into conflicts with her friends and family members, stops studying... And only her sister's serious illness, to which Kasia herself contributed, allows her to understand how much she loves the little girl and return home. to the old way of life.

The cover is different from the picture.