Jarlsblood - Saga (1). First Volume

In the early years of the 9th century, young Einar lives happily as a fisherman with his twin sister Thordis and his parents on the divided island of Tautra, nestled in the heart of the great fjord of Lade. But when the old warrior Thorstein appears at the fisherman's farm, young Einar's life takes an unexpected turn. The gray-haired Viking reveals the secret of his true origins and demands that he swear an oath to reclaim the castle and legacy of his ancestors.
Soon after, the old warrior begins preparing the boy for his quest, teaching him the use of weapons. Einar receives the sword Blood-Eye from Thorstein, a pledge of his clan's independence. But fate intervenes sooner than expected, leading the young lad to the northern island and into the service of Jarl Oyvind. Out of gratitude, Oyvind accepts him as his son. When the Jarl of the southern island presses for the expulsion of his rival Oyvind from Tautra, battle ensues.
The stepson of the Jarl of the North Island gains dominion over the small island of Tautra and succeeds Jarl Oyvind. Now a mature young man, as Jarl and leader of many warriors, Einar can finally attempt to fulfill his oath.