King Horik returns to Kattegat with a surprising proposition for Ragnar; Lagertha runs into a less than enthusiastic homecoming from her new husband; Athelstan becomes confidant to King Ecbert.

Princess Aslaug's latest prophecy comes to fruition as she readies to give birth once more. Ragnar, Horik and their new ally Lagertha set sail for Wessex - Ragnar and Horik have very different ideas about the true purpose of this trip.

Ragnar and Lagertha's fleets depart Kattegat once more for Wessex and this time they bring a group to colonize there. King Ecbert hosts the Norsemen and proposes a deal. Despite the misgivings of some of the other leaders, Ragnar leads his forces into battle once more, but this time as allies of Wessex.

Lagertha and Athelstan help to set up the Viking settlement. A mysterious wanderer arrives in Kattegat.

There is bitterness in the camp, Floki is angry over the alliance with Ecbert.

The fleet returns to Kattegat to discover tragic circumstances await.

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.