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.

Bjorn, Lagertha and Ubbe face an uncertain fate as Heahmund's loyalty is tested. Floki fights to understand the will of the gods. Ivar may have met his match.

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.

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?