One of MZB's best Darkover books. The most dangerous matrix on Darkover, embodied as a chained woman, is let loose, possibly to destroy civilization.
If you've only read MZB's Avalon books, you should give the Darkover series a try. MZB creates a fastinating, unique world with Red moons & poeple with some marvelous psychic talents. I've read almost every one of this huge series.