The Kings of Clonmel by John Flanagan
A cult has sprung up in the neighbouring country of Clonmel. The leaders of this cult call them selves The Outsiders and promise the protection of their false god in exchange for gold to "build alters." The people agree redily after some planned attacks by bandits. The people may be fool, but the Ranger's aren't.
Will and Halt travel to Clonmel to uproot the troublemakers, but they can't do it without proof. Halt has proof, but a family member complicates things. Can the Rangers get rid of the Outsiders?
**Book 8 in Ranger's Apprentice**
Previous book: Erak's Ransom
Next book: Halt's Peril