Two story lines combining into one very well-written novel: the coming-of-age story of Regis Hastur and his relationship with Danilo Syrtis (important characters from many of her books); and the tragic one of Lew Alton and the Sharra matrix. Not for the faint of heart, that one. Overall, it's about political power caught up in one ruling caste, pitted against a powerful Empire (ours, of course), and the people that affects. Throw in one mysteriously twisted character who wants the power by any means necessary, and you've got fire.
It's still not my favorite of hers, but I forgot that it was this good.