Ignore the blurb above - this is the fourth book in the Legacy of the Force Series. The review supposes you have read the first three, Betrayal, Bloodlines and Tempest.
Aaron Allston writes a great Ben Skywalker, which is good because a lot of the novel follows his solo journey as Jacen and Lumiya send him out on a mission to test whether he is a suitable Sith Apprentice. The mix of suspicion and lack of action against the fledgling Sith Lord, Jacen, is really frustrating at this point of the story - maybe even for the writers. Luke and Mara are always worrying about Jacen and his influence, but no convincing excuse comes up for their powerlessness. Much better if they just hadn't been able to detect him, and in truth the writing does try and focus on Luke's obsession with Lumiya. Just a bit too much concern and hand wringing while the Sith plot moves forward.
Worthwhile, though, especially for Ben's adventure.