The Sealed Citadel

This fantasy novel follows Cally, an apprentice in a unique sorcerer order that forbids killing. When Cally is chosen to join a delegation to meet their allies, the Lannovians, things take a deadly turn. The meeting turns into a massacre, leaving Cally and a soldier named Rowe as the only survivors. Together they uncover a conspiracy that could destroy everything, but in order to stop it, Cally may have to betray his order's beliefs.