A serial killer who slaughters campers is on the loose in Sweden. The lead detectives make a breakthrough when the killer, a cloaked figure wielding a sword and a strange mask, sends the police a video recording.

Harry Friberg photographs a mysterious lightning in the water outside the Blockhusudden. The light turns out to flow over a murder.

Ronia lives happily in her father's castle until she comes across a new playmate, Birk, in the nearby dark forest. The two explore the wilderness, braving dangerous Witchbirds and Rump-Gnomes. But when their families find out Birk and Ronia have been playing together, they forbid them to see each other again. Indeed, their fathers are competing robber chieftains and bitter enemies. Now the two spunky children must try to tear down the barriers that have kept their families apart for so long.