King Horik's and Ragnar's armies engage in battle with Jarl Borg, meanwhile is Princess Aslaug on her way to Kattegat.
The time has come for an unlikely alliance to band together for a new raid on England; a storm pushes the Viking fleet to a new destination; Ragnar and his men may have met their match.
The Wessex Viking raid is in full swing; King Ecbert finds himself facing a new kind of foe; Ragnar races to dominate in the west; Jarl Borg has his own plans in store for the future of Kattegat.
A meeting between Ragnar and Ecbert may pave the way for future compromise; Jarl Borg rules Kattegat with an iron fist; Rollo must now become the leader his people need in Ragnar's absence.
Lagertha and Ragnar unite once again and together fight to win Kattegat back from Jarl Borg. Aslaug must face the truth of her prophecies. Athelstan struggles to define his faith. Bjorn must once again make a choice.
King Horik returns to Kattegat with a surprising proposition for Ragnar. Lagertha runs into a less than enthusiastic homecoming from her new husband. Athelstan, struggling with his own inner demons, becomes confidant to King Ecbert.
Ragnar and King Horik clash over how to dispense justice to Jarl Borg; King Aelle in Wessex; Ecbert has an eye on a new alliance.
Princess Aslaug's latest prophecy comes to fruition as she readies to give birth once more; Ragnar and Horik have very different ideas about the true purpose of their trip to Wessex.
Ragnar's warriors march on to King Ecbert's villa and are met with a surprisingly vicious welcome party.
Ragnar and King Horik return to Kattegat; Ragnar places his trust in those who have stood by him.