Spoiler level: low to medium
As I mentioned in my review of the Lost Tribe of the Sith eBooks, I almost didn't read this book. I generally don't read any of the "side-story" books that aren't about the Skywalker/Solo lineage. I'm not a gamer, so I have little to no interest in Kyle Katarn and even less interest in his apprentices. But the Lost Tribe of the Sith, both in Omen and in their own eBook series, has really perked my interest in the ancient Sith, so I gave it a chance.
The book starts out in two time periods: one focusing on Jaden Korr shortly after the Legacy of the Force series, and the second focusing on two Sith dreadnoughts, the Omen and the Harbinger, 5000 years earlier. From there we see what happens to the Omen to lead to the Lost Tribe of the Sith eBook series and Fate of the Jedi: Omen book, and we see the Harbinger brought to the "present" to face Jaden Korr.
One of the reasons I was never really into the "Old Republic" stories was that the technology seems too close to the current era; for being anywhere from 5000 - 1000 years in the past, I feel like the technology levels should be radically different. I still had that problem with this book, but the characters are so enjoyable to read that I was able to forgive it. Jaden is full of self-doubt after the events of the Legacy of the Force series, losing his faith in the Force and himself, and this book is his quest to find some answers. Relin is a Jedi of the Old Republic, fighting against his own former padawan Saes, a Kaleesh (the same species as General Grievous, but without the droid parts) who has fallen to the dark side and joined the Sith, a betrayal that still hurts Relin deeply. And my favorite characters in the book are undoubtedly Khedryn and Marr, the crew of the salvage ship Junker, who end up helping Jaden on his quest.
Another advantage to the "side-story" adventures is that, since nearly all the characters were created for this book, no one is bullet proof. Not that there haven't been major deaths in the main Star Wars books, but the odds of Luke, Leia or Han being killed off are pretty low. Here there are no guarantees of anyone getting out alive.
I really enjoyed it, so I'll probably start reading more of the side-story books in the future.