I actually listened to this book and I'm glad that I did because I just know that I would've had trouble with all the Welsh words. Listening to Richard Mitchley's melodic reading of all those difficult words made the books much more accessible for me. This won the 1976 Newbery. It is also part of the Dark is Rising Sequence. Many years ago, I listened to The Dark is Rising with my sons while on a long car trip. The Dark is Rising is book 2 of the sequence. I usually don't like reading books out of sequence. This one stood alone pretty well as references to earlier books were adequately explained, but I will most likely read the sequence, well, sequentially. Over Sea, Under Stone is first, followed by The Dark is Rising; Greenwitch is third; The Grey King is fourth and Silver on the Tree is the concluding title.
Whenever I need to know what order a book belongs in almost any series, I always check the Mid-Continent Public Library's "Juvenile Series and Sequels" page (http://www.mcpl.lib.mo.us/readers/series/juv/)
Will Stanton is recovering from a serious illness; one which has robbed him of his memory of the "Old Ones" and his quest. His doctor suggests that he be sent away somewhere to recover and his mother agrees to send him to Wales to stay with her sister and brother-in-law on their sheep farm. He has recalled snatches of the riddle he is supposed to be solving and once he's viewing the mountains that surround his uncle's farm and informed of the name, he begins to recall more of the riddle. He's helped to total recall by a strange dog with silver eyes, the pet of an albino boy named Bran. Their destinies are intertwined in a way that Will never anticipated.
The world building is quite vivid and at the end, when all the pieces of the puzzle fall into place, I just laughed-out-loud at the connection to other mythologies and felt like starting the book over immediately.