The land of the silver apples - Nancy Farmer

In trying to save his sister Lucy from being thrown down a well, Jack has managed to cause an earthquake which demolishes a monastery. It appears that sometimes, the magic just doesn't quite work out but then he is, after all, only a bard-in-training!

So when Lucy is unceremoniously carried off by the Lady of the Lake, Jack gives chase and follows her through the Hollow Road which lies underground. Aided by his friend, Thorgil, the berserker, and slave girl, Pega, Jack uncovers an unexpected world of hidden caves, hobgoblins, kelpies and elves - not the enchanted sprites one would expect, but fallen angels who steal human children and torment them could this be the fate of his sister? Underground, Jack discovers that his actions will determine the fate of both worlds...