Heart of the Hill — Andrea Spalding

In Volume Three of The Summer of Magic Quartet, Adam's turn to lead the adventure has arrived. The Wise One, Myrddin, needs Adam to retrieve his staff from the Crystal Cave deep inside Glastonbury Tor. The quest grows more dangerous, however, and fear rises. Equus and Ava are far away, the Lady will not wake, and Myrddin is in human guise, unable to use magic without alerting the Dark Being. The four children are on their own. And as the Dark Being approaches, the children discover that danger can find them even in their dreams.