Jack and the Wynn

Jack is a Dutch twelve year-old boy who spends his summer school vacations with his grandparents. Despite his grandfather's warning not to venture into the dark woods at night for fear of encountering the mysterious creatures called the Wynn, Jack's curiosity gets the better of him and he is soon introduced to these magical creatures who live below ground in the woods.
Soon Jack is drawn into their way of life, their way of moving from place to place called "wiggling", and the danger they face from the evil rats. When a prophecy reveals the rising of a dangerous white rat who will bring war on the Wynn Jack finds himself made their king and facing the challenge of leading them into battle.