In the ninth and tenth centuries, King Alfred and his heirs fought to secure the survival of the last outpost of Anglo-Saxon culture by battling the ferocious Vikings, whose invading warriors had already captured and occupied three of England's four kingdoms.

In A.D. 866, Uhtred, a boy of ten and the son of a nobleman, is captured in the same battle that leaves his father dead. His captor is the Earl Ragnar, a Danish chieftain, who raises the boy as his own, teaching him the Viking ways of war. As a young man expected to partake in raids and bloody massacres of the English, he grapples with divided loyalties, torn between Ragnar, the warrior he loves like a father, and Alfred, whose piety and introspection leave him cold. It takes a terrible slaughter and the unexpected joys of marriage for Uhtred to discover his true allegiance — and to rise to his greatest challenge.