Shadow Forest, by Matt Haig
Samuel Blink is an ordinary boy, travelling in the car with his parents and sister, Martha. In one fateful event, his world is turned upside-down when a giant log falls from the sky. Now orphans, Martha and Samuel must go to live with their Aunt Eda in Norway. Sounds terrible enough - what could possibly be worse?!
But outside the house there is a Shadow Forest, full of one-eyed trolls, huldre-folk, Truth Pixies, and a witch who has a habit of stealing shadows. The stories tell of people entering the Shadow Forest, but never returning. Oh, and it's ruled by the Changemaker, an evil being. And Samuel will probably have to go in, when Martha disappears in there.
It seems Samuel might be dragged into an adventure, whether he likes it or not. Are you coming?