Ragnar and Ivar plot against the Saxons and reach a new level of understanding.

Ragnar and King Horik return to Kattegat; Ragnar places his trust in those who have stood by him.

The Viking army causes panic in the English countryside as King Ecbert and Aethelwulf plan the defense of the realm.

In Iceland, Ubbe learns the truth about Kjetill and has a difficult decision to make. Back in Norway, the battle against the Rus has had grave consequences. But re-enforcements have arrived, and Bjorn has an idea that may yet save the day.

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

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.

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.

A ferocious battle between the Vikings and the French eventually comes down to Ragnar against Rollo. The outcome will seal the fate of the two brothers.

Bjorn's fleet sails onward and launches a surprise attack. Back in Kattegat, Lagertha continues in her quest for power.

Prince Aethelwulf finds himself subject to the Vikings' battle master plan. Ecbert remains behind with a plan of his own.

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

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.

Ragnar's warriors march on to King Ecbert's villa and are met with a surprisingly vicious welcome party.

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.

Bjorn returns to Kattegat. Harald gains a measure of revenge on Olaf. In Kiev, interesting news reaches Ivar and Igor about Prince Dir.

Three Viking ships sail toward the Royal Villa of King Aelle in eastern England. Ragnar wants ransom in exchange for peace, but the king has a very different plan in mind.

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 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.

Ragnar's fleet is shipwrecked and washes up on the Wessex coast, but without enough survivors to form a credible force, Ragnar and Ivar have a difficult decision to make. Rollo meets his Viking comrades again and can't resist the urge to join Bjorn's voyage, risking his marriage and his new Frankish identity. Ragnar too is taking a risk as he carries Ivar towards the Royal Villa in Wessex – throwing himself and his son upon the mercy of 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.

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

The fleet returns to Kattegat to discover tragic circumstances await.