Richard A. Knaak had mentioned this book in our last interview, and now there is more concrete info released on his new Newszine.
Richard A. Knaak comments:

MOON OF THE SPIDER is well underway, with the first chapters already okayed by Blizzard. The story takes Zayl and Humbart to Westmarch, where he meets the noblewoman Salene Nesardo, her brother Sardak, and the giant bodyguard Polth. What starts as a request to discover the truth over her husband Riordan?s business dealings proves a far more treacherous and ancient plot. What is Lord Aldric Jitan seeking in the ruins of the estates of the Sons of Rakkis and who is Karybdus? I?ll soon be announcing the trilogy title…