Hattie Maxwell is trying to make sense of her life since the Big Split. It used to be the four of them - Mum, Dad, Ivy and Hattie - against the universe. But now it feels like she's a lone star in a big galaxy. And to make matters worse, her favourite place, Hummingbird House, is going to be demolished! Determined to stop the development, Hattie throws herself into uncovering the secrets of the house. Under a special full moon, she discovers that there is much more to the grand old mansion than first meets the eye. But will it be enough to save Hummingbird House? Or her family?