The Oathbreaker's Shadow — Amy McCulloch

In the land of Darhan, promises are bound by magic, tied into knots, and worn with pride. Those who break them are physically scarred, cast out into the desert, and stalked by vengeful shadows of their treachery.

Fifteen-year-old Raim, the best young fighter ever to train for the elite Yun guard, has worn a simple knot around his wrist for as long as he can remember. He doesn't know where it came from and barely thinks about it at all. But on the most important day of his life, when Raim agrees to give his life as a warrior to the future king, that knot bursts into flames and sears a dark mark into his skin.

Now scarred as an oathbreaker, Raim has two options: run or die.