The Night Gardener is a middle grade horror novel that takes place in 19th century England. I checked it out from the library.
Review:
Molly and Kip are two siblings who escape the Great Famine in Ireland only to find themselves orphaned and penniless. Kip doesn't know the full truth – in order to protect him, Molly told him that they'd simply gotten separated and their parents would come for them soon. In the meantime, they need money and/or a place to live, so Molly lies about her age and gets hired as the Windsor family's new maid.
The Windsor family home is creepy and strange. It and the enormous tree next to it have nearly become one. Branches have grown through the walls, and the Windsors forbid Molly and Kip to do anything about it. Molly has to clean up mysterious muddy boot prints throughout the house every day, and Kip swears that he saw someone moving around outside at night. Then there's the locked room with the green door, the one room in the house Molly isn't allowed to enter.
