We all have Christmas traditions, and one I'm sure we've shared before is Adam reading Susan Cooper's 1970s Puffin sequence The Dark Is Rising. A lot of adults of a certain age loved the books and the second one is set at Christmas time, so it's an ideal holiday to read all 5 books.
There is a beautiful set of hardbacks published by The Folio Society, who have Susan Cooper on their website reading extracts and being interviewed about the books.
The first one in the sequence is called Over Sea, Under Stone and follows 3 children as they discover treasure on the Cornish coast. They have a mysterious Great-Uncle who turns out in the later books ... well, that would be telling!