Issola by Steven Brust

In Issola, Brust returns to the top of his game, with the great snappy dialogue, sarcastic wit, and intriguing action that made the first few books in this series such winners. Vlad is still technically on the run from the Jhereg, who would love nothing better than to kill him, but when Lady Teldra finds him in his wanderings and tells him that Aliera and Morrolan have disappeared, he cannot resist the call of duty, and returns to Dzur Mountain, lair of Sethra Lavode, to confer, consult and conspire.

There's a great descriptive piece about Sethra, the undead enchantress:

"...there she was; tall, pale, undead; she had forgotten more of sorcery, even the forbidden sorcery of the ancient world, than anyone else would ever learn. She was a vampire, but it didn't seem to bother her much; and to those who told stories of her it was almost superfluous, like hearing that the guy who is going to cut your heart out plans to kick you in the shin when he's done. Her origin was in prehistory, and some had come to believe that she was the living personification of the world itself, that it would end when she ended. I doubted this myself: I mislike the idea of a living personification of being undead.
Her features were those of a Dragonlord, except that, if one looked for it (as I did), one could see hints of the Dzurlord in the shape of her ears and her eyes. She dressed in black, black, black - the only hints of color upon her today were a red stone about her neck, a yellow stone on a ring on her right hand, and the blue hilt of Iceflame at her hip. She wore enigma as if it were her due."

Aliera and Morrolan turn out to have been abducted by the Jenoine, a mysterious race which used to inhabit the world and who are responsible for the genetic manipulation that created the Dragaerans and Easterners from the same stock. They have a plot in play to regain power, and the opening gambit has been played. Vlad and Teldra journey together to the pocket universe where the Jenoine hide out, and Vlad takes on the most dangerous commission of his life, a contract to kill a goddess.

Of course, nothing ever goes exactly as planned around Vlad and his friends, and the plot goes seriously astray before the Jenoine are defeated. Along the way we get to know Lady Teldra far more deeply than we ever expected. This is a neat bit on Brust's part, as Teldra has just been a bit player throughout most of Vlad's story, appearing at Morrolan's front doors to greet his guests and make them feel comfortable. Vlad has an astonishing revelation when he finally finds out why it is that Teldra treats everyone she meets so courteously, making them feel as if she really likes them (even Easterners like Vlad) - she actually truly likes people! How astonishing.

We get a great history/mythos lesson on the world of Dragaera, delivered by Sethra when Vlad demands more background before he commits to the latest foolish and dangerous quest, whic, explains a few things about earlier events, but leaves some new questions unanswered. The "key" event in this book, which will probably play out in later installments, is the creation of the great weapon, Godslayer, which is meant for Vlad to carry. Vlad also is really turning the corner on becoming a hero, rather than the antihero we began with.