Myrren's Gift (The Quickening #1) - Fiona McIntosh

Though barely a teenager, Wyl Thirsk must now assume the role he has been destined for since birth: commander of the Morgravian army -- an awesome responsibility that calls him to the royal palace of the crown prince Celimus. Already a cruel despot who delights in the suffering of others, Celimus enjoys forcing his new general to witness his depraved "entertainments." But a kindness to a condemned witch in her final, agonizing hours earns young Thirsk a miraculous bequest, while inflaming the wrath of his liege lord.

With war looming in the north, Wyl must obey Celimus's treacherous dictates and undertake a suicidal journey to an enemy court -- armed with a mysterious power that could prove both boon and curse. For unless he accepts Myrren's gift, it will surely destroy him . . . and the land he must defend.