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

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.

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.

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.

Ragnar's plan comes to fruition. The Viking army lands on the coast of Northumbria.

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

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

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

Lagertha attempts to fulfill a long-held ambition. Ragnar negotiates an unexpected concession from King Ecbert.

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

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.

A new battle for Kattegat is on and only the gods know who will emerge victorious.

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.

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.

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

Celebrations are cut short in the aftermath of the battle at York. Ragnar Lothbrok's sons are pitted against each other as tensions reach an all-time high, and each is forced to choose a side.

The battle for Kattegat begins and, as the two armies line up to fight, the Great Heathen Army must decide between a final plea for peace or all-out war. Floki faces discord among the settlers.

Bishop Heahmund is wracked with guilt as he fights to renounce his passions. Viking will clash with Saxon on the battlefield leaving a key figure lost in the balance.

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.

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.