The Empire's hold on individual star systems doesn't leave much room for people to live free and express themselves. If an Imperial does something against you, chances are good that you're not going to have much cause for redress. Or, even if the Empire isn't directly involved, if the actions don't effect them at all, they might just not pay attention to your need. That's where the Sentinels come in. They're the ones who will stand up for the little guy during these dark times. And it's just what's covered in the Endless Vigil sourcebook for the Star Wars RPG.
So, what sort of things will you find the book? Well, like most sourcebooks, there's a whole bunch of different things. If you want new specializations for your character, you can find those. Want to try out a new race? There's some of those, too. Of course, there's plenty of new equipment and other gear. Most of it is focusing around an urban setting. For the GM, there's new droid enemies, and even rules for running your own podracing event.
Expect Endless Vigil on store shelves sometime in the 3rd quarter of this year.