12-year-old Samuel and his younger sister Martha live in Norway with their Aunt Ida and Uncle Henrik. Their house is located right next to the forest, about which there are ominous rumors. Supposedly it is full of dangerous creatures: trolls, huldras, pixies and tadwolves. But Samuel and Martha know that there is nothing dangerous there and the evil forces that recently ruled the forest have been defeated. But one day a troll boy appears on their doorstep, having fled the troll village to escape his cruel upbringing in the Tower of the Improver. Now all the residents of the house on the edge will have to think about how to hide the troll boy from prying eyes and return him to the forest, as well as how to cope with the terrible Improver.