Agnith's Promise by Chelsea Quinn Yarbro

Book Three of The Vildecaz Talents

While at the Imperial Court, Erianthee witnesses an enormous Conjure Storm that turns half of the palace complex to rubble. Afraid of what could come next, she heads for Vildecaz and home with Kloveon escorting her.
     Meanwhile, in her searches for possible clues to Duz Nimuar's location and condition, Ninianee has come upon something that sends her and her partner, Doms Guyon, back toward Vildecaz, But both sisters find their travels marked by hindrances and unexpected difficulties. When they finally arrive, they discover that malefic forces have been at work here, too, and they have little choice but to take them on, or lose their Duzky, their father, and their talents completely.

A professional writer for more than forty years, Yarbro has sold over eighty books, more than seventy works of short fiction, and more than three dozen essays, introductions, and reviews. She also composes serious music. Her first professional writing – in 1961-2 – was as a playwright for a now long-defunct children’s theater company. By the mid-60s she had switched to writing stories and hasn’t stopped yet.
     In 1997 the Transylvanian Society of Dracula bestowed a literary knighthood on Yarbro, and in 2003 the World Horror Association presented her with a Grand Master award. In 2006 the International Horror Guild enrolled her among their Living Legends, the first woman to be so honored; the Horror Writers Association gave her a Life Achievement Award in 2009. 
     A skeptical occultist for forty years, she has studied everything from alchemy to zoomancy, and in the late 1970s worked occasionally as a professional tarot card reader and palmist at the Magic Cellar in San Francisco.
     Divorced, she lives in the San Francisco Bay Area – with two cats: the irrepressible Butterscotch and Crumpet, the Gang of Two. When not busy writing, she enjoys the symphony or opera.