Krølle Bølle lives safely underground on Bornholm with his family and all the other trolls. There are rules, and one rule in particular must never be broken: do not go up to the surface, because humans are dangerous. But Krølle Bølle is a troublemaker, so he sneaks up with his sister Borra toward the human world to see what’s happening. What begins as an innocent mischief-filled outing for the two of them quickly turns into a grand adventure.