Dawn of Unity - Last of the Seekers, #1

Beliefs shattered, two magically linked are called to seek truth.  Seventeen-year-old Will escapes from prison six years after his false conviction for murder. Found by a knight who lets Will serve as a squire, Will takes the knight's mercy and follows him to war. He'll protect against infidels, proving to the kingdom he's not the monster they assume he is, and be seen kindly again. As a child, when he burned a souk, Ahmed was terrified.
Now sixteen, Ahmed is confident he's improved. Seeking to become grand vizier and bring prestige to his family is everything he thought he wanted. The sultan's test remains: bring an enemy to the capital. He heads to war believing that an enemy's capture is a small price for the sultan's blessing. They're dangerous anyway. Gems of powerful magic bring them together as kingdom and sultanate ravage each other over ignorance and religious zeal, nearing collapse.
They're mortal enemies, their monarchs say, but when Will and Ahmed meet amid fear and mistrust they learn to like each other. Their actions no longer seem right and their gems show a resolution. But who are two boys to effect change when those more likely have failed?