Over Sea, Under Stone (Mass Market Paperback)
On holiday in Cornwall, the three Drew children discover an ancient map in the attic of the house that
they are staying in. They know immediately that it is special. It is even more than that -- the key
to finding a grail, a source of power to fight the forces of evil known as the Dark. And in searching
for it themselves, the Drews put their very lives in peril.