The Danes, under Guthrum and Ragnar the Younger, capture the fortified town of Wareham. Despite this, love blossoms, and Mildrith becomes pregnant. Unbeknown to Uhtred, she bears the burden of her deceased father's debt to the church, two thousand shillings. In order to gain land and become an Ealdorman, Uhtred is persuaded by Alfred to marry Mildrith. Realizing that Uhtred will not break his word to Alfred, Brida leaves with Ragnar who is bent on revenge against Kjartan. Earl Ragnar's son, Ragnar the Younger returns from Ireland, seeking the truth about the death of Earl Ragnar. Uhtred trains the Saxon army to be ready to face the Danes after pledging his allegiance to Alfred for a year. Uhtred advises Alfred what the Danes fear and watches Alfred negotiate peace to give Wessex time to prepare for future battles. Uhtred and Brida are released and Alfred seeks a peace treaty with Guthrum and Ubba. King Æthelred and Alfred win the battle, but the king is mortally wounded, bequeathing his crown to Alfred rather than his own son, Æthelwold. There, Uhtred supplies information of an impending Danish attack, but Lord Alfred, brother of King Æthelred is uncertain whether the young couple can be trusted and advises the king to imprison them pending the outcome of the battle. Ubba and Guthrum do not believe that Uhtred is innocent of Ragnar's death, so Uhtred and Brida flee to Winchester, capital of Wessex and the last surviving Saxon kingdom. He pleads his innocence to Danish warlords Ubba and Guthrum, but he watches while they murder East Anglian King Edmund in the manner of Christian martyr Saint Sebastian.

Uhtred is blamed for the death of Earl Ragnar during a reported Saxon uprising in the North. Uhtred decides to embark on the task of regaining his lands from his uncle, Aelfric, who has usurped Uhtred's titles and inheritance and is now aligned with the Danes. Only Thyra survives and she is captured and enslaved. In young adulthood, Uhtred and Brida see Earl Ragnar killed when his hall is burned by a vengeful Kjartan and Sven. Uhtred and Brida are adopted into Ragnar's family and raised as Danes and pagans. Sven is blinded in one eye as punishment and Kjartan is banished.

The boy later saves the Earl's daughter Thyra from Sven, son of Kjartan, one of Ragnar's ship captains. Uhtred is killed, and his 10-year-old son Uhtred and a Saxon girl named Brida are taken as slaves by Ragnar. The Danes feign a retreat, leading the reserves of the Saxon army to attack, and then be flanked by a hidden force of Danes. Uhtred engages Ragnar and his Danish army at Eoferwic. In 866, Danish earl Ragnar leads a fleet of dragonships to the coast of Northumbria, where he kills the eldest son of the Saxon Lord of Bebbanburg Uhtred ( Matthew Macfadyen).

The last kingdom series in order