Leaving the safety of the marshes, a united Alfred and Uhtred prepare for a final decisive battle with the Danes. Treachery, deception and heartache follow as the fate of Wessex and England hangs in the balance.
With his advisors by his side once more, Alfred holds a witan but has already decided to follow Uhtred's advice and lead his men into one defining battle. He believes he cannot forsake England at this key moment.
Meanwhile, Guthrum tries to get information on Alfred through Æthelwold. He learns that Alfred is a clever man who believes he will win because of his faith in God. Ragnar and Brida scoff at this, but Guthrum contemplates quietly and orders Æthelwold on an assassination mission to kill Alfred.
Alfred, Uhtred, Leofric, Iseult, Brother Asser, Hilde (the nun), and Halig (Wulfhere's horse caretaker who they meet on the road when Wulfhere betrays Alfred for the Danes) travel towards Odda's estate in Defnascir (Devonshire) to start gathering Alfred's army since the Oddas have the largest fyrd. Avoiding the Roman roads which are filled with Danes, they travel by way of Lyscombe, Uhtred's home, only to find death and destruction. All the villagers have fled and a small grave is marked outside Uhtred's house with a wooden cross. The stranger's baby that was taken in lieu of Alfred's son was Uhtred's. Iseult is torn for Uhtred and the knowledge she has as a Seer. She goes to Uhtred in the woods that night so he may take her virginity, and therefore her Sight. Afterwards, Iseult finally reveals what Skorpa had whispered to her in Cornwalum: Thyra lives and is being held by Kjartan in the north.
Odda the Younger, who believes Alfred is dead, tries to make an agreement with Skorpa. But when Uhtred and Leofric, Alfred hidden amongst them, arrive to their estate and rally him to their cause, Odda refuses to believe the king still lives. His father, who has seen Alfred in the crowd, stabs his own son for his traitorous deeds. Uhtred sends Skorpa back on his way to Guthrum, who informs the Viking leader of the Saxon numbers. Guthrum asks Ragnar if he is prepared to kill his brother on the battlefield.
At St. Egbert's Stone, the gathering place for the great Saxon army, Æthelwold abandons his assassination attempt and joins Alfred at the top of the hill, watching as thousands of swords of Wessex answer the war call. Ahead of battle, Alfred, who used to fear his men did not see him as a warrior, strays from his godly sermons to deliver a passionate speech and rally his men. The English cry, "no mercy!"
As the battle commences, the Saxons let the Danes fall upon their shield wall first and then slowly advance, gaining ground. Leofric takes an axe blow to the neck and falls behind. Skorpa, realizing they are already at a disadvantage, leaves the battlefield to attack the Saxon camp where he runs down Iseult and returns to the battle, flinging her bloody head at Uhtred.
Enraged, Uhtred breaks formation and leaps over the enemy shield wall and begins killing Danes at will. Father Beocca, calling on the might of God, launches his spear towards Uhtred, who swiftly takes it and throws it into Skorpa's chest, knocking him off his horse. Ragnar asks orders from Guthrum, who shows no desire to fight back, now believing that the Saxons truly do have God on their side. But men continue to fight, and Uhtred, seeing Ragnar knocked to the ground, saves his life.
In the aftermath of the battle, Uhtred orders Leofric's grave marked as an Ealdorman and a pyre for Iseult. The Battle of Æthendun (Edington) won, Alfred admits that he is indebted to Uhtred, that Wessex is indebted. Peace is secured by Guthrum's conversion to Christianity (now King Æthelstan of East Anglia) and also with hostages including Brida and Ragnar. Brida refuses to look at Uhtred but Ragnar remains both brother and friend.
Having saved Wessex, Uhtred's path now leads back north so he can face his past.