In 1919, Henry has moved to the countryside with her parents and her baby sister, Piglet, all still scarred by the death of her brother. Alone in her head, she begins to explore her surroundings, encouraged by her only friends—characters from her favorite books. Nobody much notices when she wanders into the woods at the bottom of the garden and meets Moth, a striking witch-like woman. Together they form a bond that could help Henry save her family.