Dark Is Rising by Susan Cooper

It’s Christmas-time in the Stanton family house: presents, carol singing, good cheer. But for eleven-year-old Will Stanton something sinister has begun, inching round his subconscious, shouting silent warnings he can’t decipher. Then on Midwinter Day Will wakes up to a different world – silent, covered in snow and ancient forest, a world of another time. A world where evil lurks. Because Will is not the ordinary boy he always thought he was. He is the last of the Old Ones and the power to vanquish the evil magic of the Dark lies within him.