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 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.

A dangerously ill Ragnar returns to Kattegat, where his suspected death kicks off a scramble to succeed him. Meanwhile, Lagertha engages in a power struggle with her calculating, former second in command, Kalf. Rollo betrays his heritage and remains in Frankia. Floki pays the price for his brutality against the Christian priest.

As Ragnar and Floki remain at odds, Rollo makes great efforts in Paris to win over his new bride, Princess Gisla. Meanwhile, King Ecbert sets the task for his son Aethelwulf to rescue Queen Kwenthrith.

Floki learns of the heavy price he has paid for his actions. Rollo finds an unlikely ally in Count Odo. Bjorn has to fight a fierce opponent in the wilderness.

King Aelle goes to Wessex for Christmas and is not impressed with how family relations are developing. Rollo's future hangs in the balance.

There's an air of betrayal as those whom Odo trusts plot against him. Ecbert agrees to support Kwenthrith in Mercia. Pregnancy brings happiness to Lagertha and Kalf and a marriage is arranged.

Ragnar declares another raid on Paris at the Thing in Kattegat. Ecbert also has a journey in mind as he dispatches Aethelwulf and Alfred on a pilgrimage to Rome.

In England, King Ecbert's true ambitions are revealed as he plots to gain the crown of Mercia. The Vikings attack Paris with considerable force, but will Rollo's defenses be too much for them to overcome? Meanwhile, Harbard, the mysterious wanderer, returns and causes a stir amongst the women of Kattegat.

Defeat for the Vikings calls Ragnar's leadership into question as they evacuate their camp and move back down river. Ragnar remains inscrutable until he orders the fleet to beach at a cliff face and unveils an ingenious plan. Rollo and Gisla have news that strengthens Rollo's position at the French Court.

Tensions mount between the sons of Ragnar Lothbrok as the Vikings continue to threaten the very heart of England. As the Great Army moves to take York, with King Aethelwulf and his family still in hiding, Heahmund—the warrior bishop—must rally the Saxons to defend the Realm.

Tensions mount between the sons of Ragnar Lothbrok as the Vikings continue to threaten the very heart of England. As the Great Army moves to take York, with King Aethelwulf and his family still in hiding, Heahmund—the warrior bishop—must rally the Saxons to defend the Realm.

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.

Guided by Heahmund's visions, the Saxons devise a battle plan. Ivar the Boneless strategises as the Vikings undergo increasing pressure. Bjorn Ironside finds himself in a new territory and must convince the local commander he is a trader.

Ivar meets his match in Heahmund. Floki returns to Kattegat. Bjorn receives a lavish welcome in North Africa.

Lagertha is betrayed, and Bjorn must find a way to support the distraught queen. Floki and his settlers arrive in a new land, but it is far from what they expected.

Bjorn returns to Kattegat to learn that an attack will take place during the next full moon. Ivar must decide if he can place his trust in a former enemy on the battlefield.

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.

It’s six months after the battle of Kattegat and Bjorn is now King. As he struggles with the responsibilities of kingship, he finds he can’t rely on his mother. Ivar falls into the hands of the Kievan Rus, and in their ruthless and unpredictable ruler, Prince Oleg, he may finally have met his match.

Messengers arrive in Kattegat with news that presents Bjorn with a dilemma. Prince Oleg of Kiev seems untroubled by his conscience. Lagertha has settled into her new, peaceful life, but danger lurks nearby.

Lagertha is forced to take action. In Kiev, although Oleg continues to be friendly, Ivar is aware of the threat which Oleg poses to the vulnerable young heir to the throne. Bjorn has answered the call and come to the aid of an old enemy.

Lagertha leads her village's response to the recent attacks, but despite her best efforts, the consequences are tragic. Olaf has a bold new plan for the future of Norway. Ivar discusses Oleg's ambitions for Scandinavia.

As Norway’s Kings and Jarls arrive at Harald’s territory for the election of the King of all Norway, Olaf is certain of the result, however, it may not go as smoothly as he believes. Lagertha’s village is anxious in anticipation of another attack and she is relieved when Gunnhild arrives with re-enforcements. In Kiev, Igor and Ivar engage in subterfuge and Ivar is stunned when he encounters a ghost from his past.

Bjorn is forced to act quickly in the aftermath of the election for the king of all Norway. The Bandits attack Lagertha’s village again confident of an easy victory. However, when the defense boils down to single combat with Lagertha, victory seems less likely. In Kattegat, haunted and paranoid, Hvitserk continues to unravel.

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

Bjorn faces a difficult decision. Ubbe and Torvi leave Kattegat in search of new lands and perhaps old friends. Oleg's plans for the invasion of Scandinavia take shape. King Harald is baffled by the origin of a mysterious raiding party.