The Endonshan Chronicles Book 5: Invasion. The Endonshan Chronicles, #5

Four years ago, the Hranites breached the Wall and marched on Kenara, beginning a long and painful occupation. Korel, an Elf living on the edges of society, is determined to turn that around. He works to spark a revolution, fancying himself the hero to save all of Kenara. Instead, a few humiliating false starts land him with an unexpected group of allies and a new mission to march across the breach into Ebrun, land of the Hranites, and rescue their captured leaders.
Despite the eagerness for the task his new comrades show, he can't help but feel some doubts about some of his allies, particularly a wild Tulvan who seems of questionable reliability.