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.
Bjorn, Lagertha, and Ubbe face an uncertain fate as Heahmund’s loyalty is tested. In Iceland, Floki fights to understand the will of the gods. In Kattegat, Ivar may have met his match.
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.
A sense of doom looms over Kattegat as bloodshed ensues. The defeated army flees in the face of the victors, and a legendary warrior makes his way home.
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.
The battle for Kattegat begins and the Great Heathen Army must decide between a final plea for peace or all-out war. Floki faces discord among the settlers.
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.
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.
Ivar meets his match in Bishop Heahmund; Floki returns to Kattegat; Bjorn receives a lavish welcome in North Africa.
Guided by Bishop Heahmund's visions, the Saxons devise a battle plan. Ivar the Boneless strategizes on his own as the Vikings undergo increasing pressure. Bjorn Ironside finds himself in a new territory and must convince the local commander he is a trader and not a raider.
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 one is forced to choose a side.
Tensions mount between the sons of Ragnar Lothbrok as the Vikings continue to threaten the very heart of England.