The Crystal Cave is the first of Mary Stewart's five books based on the Arthurian legend. In it, she begins the story with Myrddin Emrys' (Merlin) childhood. The series tells the story of King Arthur and Camelot primarily by following secondary characters. The Crystal Cave is told through Myrddin Emrys' perspective.
The next book in the series is The Hollow Hills.
- Wikipedia's article on The Crystal Cave