In the middle of the forest, between mountains, lakes and robbers, lives Ronja, the daughter of the robber chief Mattis. The curious girl, who lives with her family in part of Mattis' castle, loves the wilderness and adventure. One day, Ronja meets Birk, the son of the enemy robber Borka, on her forays. When his gang begins to besiege the uninhabited part of Mattisburg Castle, the conflict between the two families hardens. But Ronja and Birk have long since formed a secret friendship. When they can no longer bear the quarrel between their families, the robber children flee into the forest and experience their very own adventure there.