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.

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.

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.

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.

Ubbe is forced into hand-to-hand combat. Floki reaches new depths and is met by a shocking sight. Bjorn sets off for Scandinavia with an old rival.

Ivar and Hvitserk lead King Harald's army to England, where King Alfred of Wessex abandons his royal villa and marches to meet the sons of Ragnar.

King Alfred falls ill as the Viking army seizes the high ground. Ingrid curses Erik. Ubbe and his people find a new world — but they're not alone.

Ubbe and the settlers open relations with the indigenous people of the new land. Ivar's strategy lures Alfred's forces into a devastating battle.

Ubbe reunites with an old friend but must pass judgment on a killer. The armies of Alfred and Ivar clash as each leader looks to his god for strength.