I am looking for a book or series that I read about 15 years ago. I can't remember all that much about it:
The man character was a boy or young man, picked up by a magician named Gwydion, and becoming an apprentice.
The overarching storyline had something to do with some kind of stones of power (think size stones to boulders) buried in the ground, forming a kind of network. This network had been tainted somehow.
There was an order of monks, known for their red hands from excessive handwashing.
I think I also remember an antagonist being freed, after being sealed inside a tree.