On holiday in Cornwall, Simon, Jane and Barney Drew discover an ancient
map in the attic of the Grey House, where they are staying with their
mysterious Great-Uncle Merry. They know immediately that it is special.
But it is much more than just a map. It is the start of a quest to find a
grail, a source of great power that could contain - or resurrect - the
powerful, age-old forces of evil in the world. And the Drews are not the
only ones searching for it.