The Runelords (Runelords, #1)

Young Prince Gaborn Val Orden of Mystarria is traveling in disguise on a journey to ask for the hand of the lovely Princess Iome of Sylvarresta when he and his warrior bodyguard spot a pair of assassins who have set their sights on the princess's father. The pair races to warn the king of the impending danger and realizes that more than the royal family is at risk--the very fate of the Earth is in jeopardy.