The Gilded Chain — Dave Duncan

As unwanted, rebellious boys, they find refuge in Ironhall...Years later they emerge as the finest swordsmen in the realm -- THE KING'S BLADES

A magical ritual of a sword through the heart binds teach to his ward--if not the king himself, then to whomever else the monarch designates-with absolute loyalty. And the greatest Blade of them all was--and is--Sir Durendal.

But a lifelong dream of protecting his beloved liege from enemies, traitors, and monsters is dashed to bits when Durendal is bonded till death to an effete noble fop at his king's orders. Yet Destiny has many strange and inscrutable plans for the young knight--for a mission, a contest, and, perhaps, a treasure await him in a faraway land. But he soon finds himself enmeshed in treason and foul intrigues, compelled to betray the king he had hoped to serve. The Blades have ways to protect their own, but death and madness haunt the path to salvation and few ever return unscathed.