The Legend of Prince Valiant

Dylan has seized Greystone, prompting King Arthur to send an army to reclaim this castle for the side of good. The king allows Valiant to take part in the campaign despite his fear that the prince won't be able to keep his hatred in check. It turns out that Arthur should be more worried about Sir Gawain, who is concealing a serious injury in order to stay in command of Camelot's army. How can Dylan be defeated if Gawain lacks the strength to lead?