Preparations for the Paris raid pick up speed, and Rollo thinks about the Seer's prophecy.

The Viking fleet causes panic in Paris. The Emperor Charles declares he will remain in the city.

Paris is hit with a second assault. Emperor Charles needs to make a difficult decision.

With one last chance to take Paris, Ragnar, and his Vikings troops take a daring chance. Ragnar asks Bjorn for a favor that could change the course of Viking history.

A dangerously ill Ragnar returns to Kattegat, where his suspected death kicks off a scramble to succeed him. Meanwhile, Lagertha engages in a power struggle with her calculating, former second in command, Kalf. Rollo betrays his heritage and remains in Frankia. Floki pays the price for his brutality against the Christian priest.

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.

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.