Over sea, under stone is a "contemporary" fantasy, with an emphasis on contemporary. There isn't much to do with magic. However, it does focus on the quest for holy grail. Some kids happen to stumble upon a map of the location. However, others are keen to get it from them. They try to pass themselves off as the good guys, however, we see right through them. The kids, however, make a number of mistakes. They trust some people they shouldn't, and don't do things they should. They suffer a number of close calls, but in the end things work out well. There are some ties to King Arthur and the battle of good versus evil. However, for now, it is mostly a treasure hunt.
While Over Sea, Under Stone was a nice contemporary book with fantasy elements, Dark Is Rising goes all in with good vs. evil fantasy. A kid is an "old one" and must help protect the world from evil. There are other old ones that have been around for centuries. It is mostly fantastical and very little contemporary. I struggled to keep going with the book.
