Thom Madley: Marco's Pendulum (UK 2006)
From the Publisher:
When Marco is dumped in Glastonbury to stay with his weird hippy grandparents for the summer, he's sure he's going to hate it. But he soon starts to recognise the magic of the place - the magic that a development company is planning to exploit and, his grandparents are sure, destroy the process. With his mysterious newfound talent for dowsing, Marco is quickly drawn into the dangerous struggle to protect the ancient mysticism of Glastonbury.
Thom Madley: Marco's Pendulum. Is the Holy Grail buried in Glastonbury, or something much darker? Usborne; ISBN: 0746067607 (April, 2006), 456 p., £6.99.