Books like Vosper's Revenge

Vosper's Revenge is the final book in Kristian Alva's popular "Dragon Stones" trilogy. As the races of Durn stand on the brink of war, the power-hungry emperor plans his conquest of the entire continent. The dragon riders are fragmented. They have been scattered across the land; weakened by the discovery of a traitor in their own ranks. Are the riders strong enough to defeat Vosper before he destroys them all? Audience: Young Adult Fantasy