The battle begins between Ragnar and King Horik's forces against Jarl Borg; Princess Aslaug makes 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.

King Ecbert finds himself facing an entirely new kind of foe; Ragnar races to dominate in the west; Jarl Borg has his own plans in store for the future of Kattegat.

Ragnar and Ecbert come face to face; 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 to try 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 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 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.

Ragnar and Lagertha's fleets depart Kattegat once more for Wessex and this time they bring a group to colonize there. King Ecbert hosts the Norsemen and proposes a deal. Despite the misgivings of some of the other leaders, Ragnar leads his forces into battle once more, but this time as allies of Wessex.

Lagertha and Athelstan help to set up the Viking settlement. A mysterious wanderer arrives in Kattegat.

King Ecbert visits the developing Viking settlement as the first harvest is sown.

There is bitterness in the camp, Floki is angry over the alliance with Ecbert.

The fleet returns to Kattegat to discover tragic circumstances await.

Preparations for the Paris raid pick up speed, and Rollo thinks about the Seer's prophecy.

The Viking fleet causes panic in Paris. The Emperor Charles declares he will remain in the city.

The Viking army sets out and Paris goes into lockdown as the army prepares the defense.

Paris is hit with a second assault. Emperor Charles needs to make a difficult decision.

With one last chance to take Paris, Ragnar, and his Vikings troops take a daring chance. Ragnar asks Bjorn for a favor that could change the course of Viking history.