The third book in Mary Stewart's brilliant Merlin Trilogy, The Last Enchantment will not disappoint. It picks up where the previous two novels left off, following Merlin The Enchanter as he guides a young Arthur through the beginnings of his reign, the troubles with his sisters, battles with the Saxons, and intrigue in plenty.
The beauty of Stewart's work here, is that she ties Merlin - a character who is synonymous with magic - to a world in which, although magic features, Merlin is a man. He gets by on wit and luck as often as by magic, and is a thoroughly enjoyable character to read about. She also brings links (as close as she can) to real places and real events, making this a volume which gives you some clue as to how it might have been. Or at least how it should have been.
If you have read The Crystal Cave and the Hollow Hills, you won't be disappointed. If you haven't start there and work your way here for maximum enjoyment. If you've read the books before, then pick them up again - I just have after four or five years, and they are just as good a second time round!