The Sea Of Trolls by Fannie Farmer

Set in a richly imagined world inspired by Norse mythology, the story follows Jack, a young Saxon boy, who embarks on a perilous journey after being captured by Viking berserkers. Alongside his sister Lucy and a mysterious bard, Jack must navigate through treacherous lands filled with trolls, dragons, and magical creatures to fulfill a prophecy and save his sister from a terrible fate. As he learns the power of storytelling and the importance of courage, Jack discovers his own strength and the true meaning of heroism.