A Spell of Winter: Helen Dunmore

Cathy and her brother, Rob, don't know why they have been abandoned by their parents. Alone in their grandfather's decaying country house, they roam the wild grounds freely with minds attuned to the rural wilderness. Lost in their own private world, they seek and find new lines to cross.

But as the First World War draws closer, crimes both big and small threaten the delicate refuge they have built. Cathy will do anything to protect their dark Eden from anyone, or anything, that threatens to destroy it.