I found this in an Opportunity shop, it used to belong to one of my university friends, Jennifer Yearsly. It is all about the Drew children, Simon, Jane, and Barney who find an old map in a hidden room while summering at the Grey House in Cornwall. Along with their Great-Uncle Merry, they become embroiled in a web of intrigue that surrounds an Arthurian legend. In the beginning the story seems a bit slow and tedious as the plot and setting dominate, but it gets better. Barney has the youthful vulnerability of the youngest sibling, Jane is the the sensible and soft-spoken middle child, and Simon speaks with the assurance and bravado of the older brother. This is the first in a five book series called The Dark Rising. This first story in the series is much more in the vein of a mystery than the later novels in the sequence which fall much more into the fantasy category.