"Lysy" (Bald) is the leader of a youth gang. Tall, strong boys from the upper grades of primary school use their physical advantage to terrorize younger and weaker students. They extort money from them, beat them, make them carry schoolbags, and humiliate them in various ways. And only one girl - Kaska - dares to oppose them. Intelligent, full of initiative, stubborn and determined to do everything, a girl from a parallel class intends to fight Lysy and his partners. Over time, a group of colleagues gathers around her, who will also be ready to defend the weaker ones. Kaska has two brothers, Andrzej, who is a year younger, and 7-year-old Jarek. They are also involved in the fight against Lysy.