Here's the series summary from wookieepedia as well.
'It has been two years since the death of Darth Caedus. Chief of State Natasi Daala has ushered the Galactic Alliance into a time of unprecented calm, and now the entire galaxy stands poised to freely embrace the same enduring peace that Jacen Solo once sought to impose as a Sith Lord.'
In this new era, Luke Skywalker finds himself battling control of the very order he founded. After Jacen's fall to the dark side, much of the galaxy sees Jedi Knights as rogue soldiers too dangerous and unstable to leave unfettered. It is a view shared by Chief Daala, who has sworn to bring the order under government control--or disband it entirely.
But the greatest threat to the Jedi remains unseen, a faceless menace even more lethal and insidious than the Sith who have plagued the Jedi for millennia. Awakened by Jacen Solo during his five-year odyseey, this hidden peril is reaching out from the darkest corner of the galaxy, assaulting Jedi Knights in ways that even Luke has yet to perceive--but which he must quickly thwart if he is to have any hope of redeeming the New Jedi Order.
The last paragraph is the most interesting and I'm curious as to who this new enemey is.