The Burning Land / Hair, David.

The Falconsare knights of the Vestal Order, pledged to use their powers to protect the Empire of Talmont from the bestial Vyr and the carnage they have unleashed upon the world.
When the Falcons take a Vyr alive, they go against the protocols of the Vestal Order and interrogate him. They are horrified to learn that the Empire's worst enemy may not be the Vyr, but the Vestal Order itself.
Led by the indomitable Romara Challys, the Falcons go rogue, their quest for the truth taking them through burning forests, lost ruins and the uncanny traces of a dying race, desperate to find answers before it's too late.
But by setting themselves against their own Order, the Falcons face all the terrifying resources of the Empire's most deadly military power. Fanatical lictors, vengeful knights, and the greatest warrior in the world are on their heels, as they seek the answers they need . . . before time runs out for everyone.