Stronghold

A mysterious and seemingly unstoppable invasion force swarms across the land. For Andry it signals the start of a nightmare made real, the horrifying fulfillment of his long ago visions of his homeland in flames, and he will draw upon even the forbidden sorcerer's magic in an attempt to destroy the enemy which is bent on the extermination of all Sunrunners. Rohan and his son Pol have to fight the enemy with every weapon at their command. This invasion may prove not only the end of their dream of an unbreakable peace but the beginning of the end of their entire world ... (adapted from the back cover of the first edition)