When Hilda wakes up in the body of a troll, she must use her wits and courage to get back home, become human again and save the city of Trolberg.

After the events of The Stone Forest, Hilda and Baba switch species, with Baba turning into a human, and Hilda turning into a troll. Hilda goes on an adventure to find a way to bring herself back human again, with her mother, Johanna, trying to find for her in the mountains. Hilda must find a way to get herself back home as a human, and prevent the citizens of Trolberg from being invaded by trolls.