Molly is a young Irish girl fleeing the potato famine with her brother Kip. She takes a position as a housekeeper at the spooky Windsor estate. Gifted with a vivid imagination, she frequently tells stories to protect herself and Kip from the harsh reality of their parents' disappearance. She feels responsible for her brother's physical and emotional well-being, hiding uncomfortable truths to keep him hopeful.

Kip is Molly's younger brother who works in the Windsor family's stables. Born with a disability that affects his leg, he uses a wooden crutch to move around but possesses immense internal strength. He is observant and deeply unsettled by the strange occurrences on the island, often questioning the stories his sister tells him.

Constance is the formidable matriarch of the Windsor house. Raised in high society, she struggles with her current circumstances and her husband's poor financial choices. She exhibits a stern confidence that subverts typical Victorian expectations, though her physical health rapidly declines while living on the island.

Mr. Windsor is the timid and anxious head of the household. His poor business investments and desperate desire to provide for his family lead them to the cursed estate in the Sourwoods. He behaves far less assertively than expected of a man of his standing, often deferring to his wife or cowering from his problems.

Hester is an older traveling storyteller who roams the countryside collecting and trading tales. She operates outside societal norms, using her reputation to secure fair prices and free lodging. Her vast knowledge of local legends makes her perceptive, easily seeing through the fabrications of others.

The Night Man is a pale, terrifying figure dressed in black who stalks the halls of the Windsor manor while the inhabitants sleep. He carries a watering can and tends to the massive, ominous tree growing into the house. He possesses strange, wind-manipulating abilities and relentlessly protects the tree.

Penny is the youngest child of the Windsor family. Bored and isolated in the gloomy house, she eagerly listens to Molly's magical stories. Her health and appearance have dulled since moving to the island, and she spends her time reading mysterious books about a fictionalized princess version of herself.

Alistair is the older Windsor child who frequently bullies those he perceives as weaker. He longs for the time before his father lost their wealth and acts out his frustrations through meanness and an obsession with sweets. He uses cruelty to mask his own lack of bravery.

Dr. Crouch is an arrogant, opinionated Victorian physician. He firmly dismisses anything related to magic or spirits as nonsense and represents the strict moral and scientific righteousness of the period. He views poor or Irish individuals with barely concealed contempt.

Fig is a ruthless criminal creditor operating in the Victorian middle class. He preys on desperate people and uses intimidation to collect debts, showing no hesitation in threatening the Windsor family.

Stubbs is a dangerous criminal who functions as muscle alongside Fig. He operates outside honest business practices, perfectly willing to use force against vulnerable families to secure payments.