The Winter King is a retelling of King Arthur, but has a fair amount of differences from the classic Knights of the Round Table fables. The story takes place in Dark Ages Britain. Merlin has vanished. Arthur, the bastard son of Uther Pendragon, has been banished, and King Uther's legal son has died. The son's wife is about to give birth and if it's a son, Uther will have a new heir.
After a difficult labor, Morgan, Arthur's full sister and therefore another bastard of Uther, step in and helps get the child out. It is a boy, but the struggle to get him out left him with a lame foot. Regardless, he is Uther's new heir and is named after his father, Mordred.
It's a darker more realistic take on the familiar storyline, kinda like the 2004 King Arthur movie was supposed to be. One part I found interesting was, given I had read Mists of Avalon last year, was the different role of religion. The book is being written by a druid who grew up in Avalon and we see him learn to be a warrior and fight for Arthur in this book. But at the time of his writing he is a Christian monk.
Mists of Avalon highlighted the conflict between the local religion and the influx of Christianity, primarily argued for by Gwenhwyfar. This book goes back to the Guinevere spelling. In this book, she is actually a follower of Isis.
Another interesting choice is the character of Lancelot, who is quite simply a douche-bag.
I assume over the course of the three books we'll see how Christianity gains more ground. I think I'll read more of the series, but am undecided on when.