Vector is actually a storyline that spanned the four major Star Wars comic lines of the time in which it was written. That included Knights of the Old Republic, set 4000 years before the movies;
Celeste Morne is a Jedi Knight from 4,000 years in the past, a period presented in Star Wars Knights of the Old Republic. She was unfortunate to be possessed by a Sith talisman that held the essence of Darth Karness Muur. Through the talisman, Muur is hoping to take over Celeste's body so he can try and rule the galaxy once more. Her willpower is all that stands in the way. She was able to get herself placed in stasis in order to try and protect everyone. Four thousand years later, she was found by the new Darth Vader. After realizing, he could not bring her under his rule as an apprentice, he trapped her on a desolate planet.
Decades later, she is found by a group of rebels led my Luke Skywalker and his friends. They are shocked to find that a series of Imperial vessels recently crash-landed on the planet while there seemed to be no signs of life. That all quickly changes with the arrival of feral creatures that seem to be led by a mysterious Jedi woman. It turns out that it is Celeste. She quickly does what she can to drive off the rebels after a battle when she realizes that Luke and his sister Leia Organa have a certain amount of a appeal for the spirit of Muur. Unfortunately, a lurking Stardestroyer provides Muur with an opportunity to get off-planet, though Celeste keeps the vessel isolated, at least for a century.
That is when the vessel is approached by the Mynock, the smuggling vessel used by Cade Skywalker and his friends as they make their way to Coroscant in the hopes of assassinating Emperor Darth Krayt. After being attacked my more feral creatures, Cade and his friends, including a childhood friend who is now serving with the Imperial Knights, meet Celeste. Unfortunately, Cade and his childhood friend are bitten by the creatures.
Celeste informs them that the bites will cause them to be infected with a disease. It is this disease that causes the feral creatures, who were once normal sentient beings. There is no cure ... well, there isn't a cure for most people. Thanks to Cade's special skills with the Force, he is able to provide a solution, allowing him and his team to team up with Celeste to go after Krayt.
Celeste claims that she is willing to help because she sees an inner strength in Cade because he seems to spur power, something that will help keep him away from the Dark Side while possibly providing an end to her trapped status with the talisman. In reality, her willpower is breaking down and Muur is hoping to use this as an opportunity to merge with Krayt and gain ultimate power.
The meeting between the two forces (Sith vs. Cade's team) proves to be quite intense and is filled with surprises that will likely change the direction in which Star Wars Legacy is heading.
This was a really interesting plotline. It can be really interesting to read these major event works, though, I always feel a little cheated because I think they are more a marketing ploy to get you to read more of the titles from a franchise. It works because I just ordered the Star Wars Rebellion books.
I did find the presentation to be a little bit choppy. Characters/events lurch a bit shifting time and location at the turn of a page, leaving the reader a bit confused because it is not always clear things have moved. With that said, it was definitely worth the read.