The Crystal Cave, by Mary Stewart
I don't know how this book came to be in my book collection actually, but I found it on a shelf, looking well-worn and needing new eyes on it. I found it on my shelf and picked it up awhile ago when looking for something new to read. Probably it was loaned or given to me by my mother many years ago; she's always liked Arthurian legend.
It was the story of Merlin's youth and how he came into his powers and legend. It stops right before Arthur is born. I was startled to discover on Amazon that it is the first of a series of books -- shows how little I knew about it before I picked it up.
I enjoyed this book. It was hard to follow at times, very wordy, but an interesting approach to an old legend. I don't know if I'll ever look for the following books in the series though.