Star Wars: Splinter of the Mind's Eye #1

Deep in the swamplands of the planet Mimban lies a powerful crystal, capable of giving its possessor an invincible mastery of the Force. In the right hands, it could save the galaxy. But in the wrong hands, it could destroy it. While the explosion of the first Death Star still reverberates through the cosmos, Luke Skywalker finds that the war he thought he won was only a battle, and that the dark side of the Force still stalks the galaxy.