"The Daylight War" is my favorite novel yet by Peter V. Brett, and it's one of the best fantasy novels that I've read. It describes how, after the events of "The Desert Spear," Arlen and Jardir prepare for the coming new moon.
The rest of this review will not contain spoilers about "The Daylight War" (though it will describe plenty of broad trends and things that you learn very early on), but it will assume that you have read the previous two books and spoil those.