Allies (Star Wars: Fate of the Jedi - Legends)

Only one thing could unite the forces of Jedi and Sith: an enemy far deadlier than both.
 
What began as a quest for truth has become a struggle for survival for Luke Skywalker and his son, Ben. They have used the secrets of the Mind Walkers to speak with the spirits of the fallen, risking their lives in the process. They have faced a team of Sith assassins and beaten the odds to destroy them. And now the death squad’s sole survivor, Sith apprentice Vestara Khai, has summoned an entire fleet of Sith frigates to engage the embattled father and son. But the dark warriors come bearing a surprising proposition that will bring Jedi and Sith together in an unprecedented alliance against an adversary more ancient and alien than they can imagine. For in the treacherous web of black holes that is the Maw, the Skywalkers and their Sith allies will have to fight an unimaginable evil, and Luke will be rocked by a staggering truth.