A dark night when the thunder goes and the wild whites fly, the girl Ronja is born in Mattisborgen, the first child of the robber chief Mattis and his wife Lovis. When Mattis shows her daughter for her robber band, a gigantic flash hits the castle and cleaves it and the whole mountain from top to bottom. Ronja grows up to a brave little robber girl and when she is big enough she is sent out to the Mattis forest to get to know all the dangers that lurk there. There are weeping warriors and rumps, the dangerous river and the horrible devil's gap. But Mattis doesn't even know the biggest danger - in the forest there is also Birk, son of Matti's arch-enemy Borka ...