Ad lit.org: Reading Discussion Guide: The Sea of Trolls by Nancy Farmer

In A.D. 793, eleven-year-old Jack leaves his family farm to become an apprentice to the Bard, a druid from Ireland, who is assigned to his Saxon village. At first, he is unsure of his duties, and is puzzled when the Bard experiences a nightmare that Jack later learns foreshadows a rollicking and dangerous adventure-quest with the Northmen, led by Ivar the Boneless. Jack and his little sister, Lucy, are snatched by the berserkers and enslaved by Olaf One-Brow and his shipmate, Thorgil. Accompanied by a crow called Bold Heart, the two children encounter a sea of characters: humans and animals, trolls and half-trolls. There are surprises around every corner, and just when doom seems imminent, there is a bit of humor to lighten the suspense. Steeped in Norse mythology and Saxon history, The story brings Jack and Lucy full circle, but with a surprise ending.