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.

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.

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.

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

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.