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.

The army leaders consider their options in the aftermath of the battle. In Floki's camp, all hopes of binding the community together are dashed as tragedy unfolds.

A sense of doom looms over Kattegat as bloodshed ensues. The defeated army flees in the face of the victors. A legendary warrior makes his way home.

Ivar is crowned the new king of Kattegat just in time to welcome Rollo home. Bjorn, Lagertha and Ubbe must rely on unsteady alliances to survive.

Heahmund must try to convince King Alfred that his actions are in defense of the Crown. Ubbe and Torvi strengthen the position of the Vikings but not all in the Viking camp support their strategy. Another settler disappears in Iceland.

As the celebrations for Ivar continue in Kattegat, grief hits Iceland and Floki must now make a fated decision. Harald's army approaches Wessex. A conspiracy grows against King Alfred.

Bjorn achieves one of Ragnar's dreams. Ivar hatches a new plan while preparing for a divine arrival. In Iceland, a settler returns in a terrible state. King Alfred faces his greatest threat yet.

An unexpected turn amongst the settlers leaves Floki powerless. King Alfred confronts Judith. In York, Bjorn must strike a deal with Harald. Wessex is once again threatened by a Viking force, but who will lead the Saxon army to defend the Realm?

Hvitserk is severely tested. Floki makes an amazing discovery. Freydis gives Ivar a surprise. Ubbe negotiates with the three Danish Kings that have massed their armies in Reading, but the negotiations may have a perilous outcome.

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.

In Iceland, Ubbe and Torvi finally meet a mysterious wanderer. Bjorn is forced to re-think who his enemies are when Erik returns from a scouting mission with worrying information. Bjorn will need allies, but he may not be able to convince his old foe, King Harald, to join forces in the face of the new threat. Ivar is reunited with someone close to him.

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.

Ubbe persuades the settlers in Iceland to embark on a voyage of exploration. The defeat of the Rus creates power vacuums in both Kattegat and Kiev.

The election for Kattegat's new ruler is held, but a surprise visitor disrupts the proceedings. Ivar puts his plan to overthrow Oleg into action.

As his enemies scheme for power, Harald prepares for his coronation and chooses a queen. Ubbe's party reaches shore — but not the one they're seeking.

Factions in Greenland spill blood, driving Ubbe's company away. Troops under Ivar and Dir seize Kiev for Prince Igor. Gunnhild makes a fateful choice.