Bearers of the Black Staff

This NYT bestseller depicts a post-apocalyptic world where humankind is extinct after a demon-led war. The survivors live in a magical valley that shields them from the horrors beyond. However, when the magic protection vanishes, unknown predators start stalking the valley. Sider Ament, the last surviving descendant of the Knights of the Word, teams up with two young Trackers and an Elf princess to defend their ancestral home. The wielder of the black staff is looking for a successor to fight the rising wave of evil.