This is actually a book combining what were two different novels, Web of Light, centered on Domaris, Web of Light, and the sequel about her sister Deoris, Web of Darkness. Reviews claim this forms the backstory for Bradley's Avalon series. Not really. When this book came out in 1983, there was no mention or tie to Mists of Avalon within it, I only heard about such a tie when I saw reviews for The Fall of Atlantis. For that matter, the book that ties this in with her Avalon series wasn't even credited to MZB, but Diana Paxson. (And by the way despite the title this isn't set in Atlantis, but a supposedly even earlier civilization.) So this book should stand on its own terms. And on its own terms, while I find it entertaining I don't think (or Avalon) it can light a candle next to MZB's Darkover books. Still, it does say something that I can still remember a book I first read in my teens decades later. I was particularly taken by the relationship between the sisters. I found Deoris, the "dark" one of the pair, by far the most interesting.