The battle begins between Ragnar and King Horik's forces against Jarl Borg. Borg is joined by Rollo, and this Viking clash pits brother against brother. There can only be one victor. Meanwhile, Princess Aslaug makes her way to Kattegat and brings with her a surprise that leaves Ragnar in a difficult predicament.

Four peaceful years have since passed with Ragnar as Earl. The time has come for an unlikely alliance to band together in pursuit of a common goal - a new raid on England. A storm pushes the Viking fleet to a new destination, and on the beaches of Wessex, Ragnar and his men may have met their match.

The Wessex Viking raid is in full swing and King Ecbert finds himself facing an entirely new kind of foe. While Ragnar races to dominate in the West, Jarl Borg has his own plans in store for the future of Kattegat.

A meeting between two great men may pave the way for future compromise as Ragnar and Ecbert come face to face. Jarl Borg now rules Kattegat and with an iron fist and Rollo must now become the leader his people need in Ragnar's absence.

Lagertha and Ragnar unite once again; 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. In Wessex, King Aelle arrives and 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, Horik and their new ally Lagertha set sail for Wessex - Ragnar and Horik have very different ideas about the true purpose of this trip.

Ragnar's Viking warriors march on to King Ecbert's villa and are met with a surprisingly vicious welcome party along the way. After a bloody battle both sides must come to new terms

Ragnar and King Horik return to Kattegat and the final showdown between two Viking leaders is at hand. Ragnar has placed his trust in those who have stood by him and now the time has come for new alliances to be made.