The Grey King: The Dark is Rising sequence by Susan Cooper
You are the last of the Old Ones to be born on Earth and I have been waiting for you.'
Following a serious illness, Will is sent to convalesce in Wales. There he meets Bran, a mysterious boy, who helps Will in his quest to find the golden harp and confront the most dangerous power of the Dark he has yet encountered: the Grey King.
The fourth book in the classic `The Dark is Rising' sequence, `The Grey King' was awarded the Newbery Medal.