Allies by Christie Golden

This book seems to explain a lot--almost too much, too quickly. The Jedi seem to be driven mad by Abeloth, a monstrous being in the Maw who may have defeated Callista at one point. Luke joins the Sith (from the Lost Tribe) in a tenuous truce. Daala's behavior gets worse and worse, and the Jedi on Coruscant more beleaguered. I'm intrigued to see where the series goes from here.