The Sorcerer of the North: Ranger's Apprentice, Book 5

Years have passed since Will led his people to victory in The Battle for Skandia, and now he oversees a peaceful fief in the south. Will's quiet days come to a sudden end, however, when troubling news arrives from the north. The king has been poisoned, and Will's abilities are desperately needed to track down the culprit - who's rumored to be an evil wizard.