The Tournament at Gorlan (Ranger's Apprentice: The Early Years Book 1)

Series:

When Halt and Crowley discover that the ambitious Morgarath has been infiltrating the Rangers in order to corrupt the corps and, ultimately, steal the throne, they seek a royal warrant to stop him before it is too late. Yet when Halt and Crowley arrive in Gorlan, they discover just how close Morgarath's scheme is to taking root.