Star Wars: The Eye of Darkness (The High Republic) (Star Wars: The High Republic Book 4) by George Mann

The galaxy is divided. Following the shocking destruction of Starlight Beacon, the Nihil have established an impenetrable barrier called the Stormwall around part of the Outer Rim, where Marchion Ro rules and his followers wreak havoc at his every whim. Jedi trapped behind enemy lines, including Avar Kriss, must fight to help the worlds being pillaged by the Nihil while staying one step ahead of the marauders and their Nameless terrors.
 
Outside the Nihil’s so-called Occlusion Zone, Elzar Mann, Bell Zettifar, and the other Jedi work alongside the Republic to reach the worlds that have been cut off from the rest of the galaxy. But every attempt to breach the Stormwall has failed, and even communication across the barrier is impossible. The failures and losses weigh heavily upon both Elzar and Bell as they search desperately for a solution.
 
But even if the Republic and Jedi forces manage to breach the Stormwall, how can the Jedi fight back against the Nameless creatures that prey on the Jedi’s connection to the Force? And what other horrors does Marchion Ro have in store? As desperation for both the Jedi and the Republic grows, any hope of reuniting the galaxy could be all but extinguished. . . .