On the night Ronia was born, a thunderstorm raged over the mountain, but in Matt's castle and among his band of robbers there was only joy — for Matt now had a spirited little black-haired daughter. Soon Ronia learns to dance and yell with the robbers, but it is alone in the forest that she feels truly at home.

Then one day Ronia meets Birk, the son of Matt's arch-enemy. Soon after Ronia and Birk become friends the worst quarrel ever between the rivals bands erupts, and Ronia and Birk are right in the middle.