Star Wars: The Dark Nest Trilogy - Legends (abridged)

Luke Skywalker is worried: A handful of Jedi Knights, including his nephew and niece, Jaina and Jacen Solo, have disappeared into the Unknown Regions in response to a strange cry for help that only they could hear. Now the alien Chiss have angrily lodged a formal complaint, accusing the missing Jedi of meddling in a border dispute between the Chiss and an unidentified aggressor.

Despite being given new worlds to populate, the insectoid Killiks have not found peace. An unknown enemy has been attacking the new nests and the Killiks hold the Jedi responsible. Traveling back to the Unknown Regions to unravel the mystery, the Skywalkers and Solos discover an evil far more familiar than they ever expected...and even more terrifying.

The Chiss-Killik border war is threatening to engulf the entire galaxy and raising the awful specter of Killiks sweeping across space to absorb all living creatures into a single hive mind. Leia's newly acquired Jedi skills will be put to the ultimate test in the coming life-and-death battle. As for Luke, he will have to prove, in a lightning display of Force strength and swordplay, that he is beyond a doubt the greatest Jedi Master in the galaxy.