The Danes invade Wessex and Uhtred is driven to hiding in the marshlands with King Alfred. With the life of Alfred's child hanging in the balance, a bond is finally struck between the pagan warrior and his pious king.
Leofric and Uhtred share an ale the night before their duel, admitting respect and friendship for one another. Alfred offers Uhtred one last chance for redemption, but Uhtred refuses to give Iseult up knowing she would be killed should she return to Cornwalum.
As a crowd gathers for the impending duel, Brida walks among them, observing, before taking off on horseback and signaling along the forest's edge. An army of Danes slowly emerges from the trees, ready to invade Winchester.
Meanwhile, the fight between the two warriors rages on, an even match at best. Alfred, who does not wish to see bloodshed on the feast day of Saint Chad, walks away. Leofric and Uhtred have discarded their weapons at this point, throwing punches at each other, when the Danes have entered the city walls. Leofric is quick to declare the end of their fight as they flee in the ensuing panic.
Guthrum gains entry into the palace but Alfred is nowhere to be found. Æthelwold has remained behind and seizes this opportunity to confront Guthrum has the real king of Wessex. Guthrum is less than impressed and strikes Æthelwold down. However, what Guthrum is impressed by is the "magic" of Alfred's scrolls. "Words without sound, voices without people", Guthrum wants to use this knowledge to his advantage like Alfred has.
Uhtred, Leofric, and Iseult hide in the rafters of a mill house when Vikings burst in and begin raping a nun. Iseult, unable to look away, hops down from above to stab the Dane and save the nun's life. The group's number is now four, and they must make their way out of the city by pretending to be two Danes and two hostages. They are almost out until Brida recognizes Uhtred and confronts him. She is not friendly, but allows them to escape. They make their way to the marshlands when a small party of Danes chases after a group of priests. Uhtred and Leofric fend off the attackers and help everyone escape by boat. The priest they manage to save is none other than Alfred, to Uhtred's chagrin. Although Uhtred is quick to remind him that like every other kingdom before it, Wessex has fallen and he is now king of nothing.
In the safe haven of the Athelney marshes, both Alfred and his infant son, Edward, grow sicker. Alfred reveals to Uhtred that to save Wessex from crumbling bit to bit at the hands of the Danes, there must be a single, defining battle that will determine the fateful outcome of either nation. To do this, Alfred dispatches his priests in every direction to inform his enemies of his current whereabouts.
Iseult prepares herbal tonics for Alfred's hemorrhoids which work well enough that he can eat meat again. But another way must be found for Edward--a pagan way which Ælswith is not keen on. Iseult predicts the child only has one night left and Alfred, whose fate as a king is tied to fate as a father, is desperate to save him. Iseult warns Uhtred that to save one life, another must be taken. When they awake the next morning, the baby is magically healed. Alfred, overcome with joy, is deaf to Father Beocca's exaltations that their prayers were answered by God. Yet Iseult weeps for the stranger's baby.
Uhtred excursions and devises a plan: kill all Skorpa's men who are currently water-bound and force the remainder to join forces with Guthrum, leading to the penultimate battle. They goad Skorpa's men into the deep marshes, letting the wetlands trap them before they attack. In the sunset, they look on at the burning long ships with renewed hope for a Wessex retaliation.