Ragnar and Floki are still at odds; Rollo makes great attempts to win over his new bride, Princess Gisla; Bjorn's survival skills are put to the test; King Ecbert sets the task for his son Aethelwulf to rescue Queen Kwenthrith.
Ragnar reveals his plan to raid Paris again, and although the fleet is storm-tossed as it sets out, the challenge lies in Frankia where Rollo awaits. Meanwhile, Ecbert dispatches Aethelwulf and Alfred on a pilgrimage to Rome.
Now aware that Rollo has betrayed him, Ragnar carries out his plan of attack, which has dire consequences. Ecbert is given an offer from Prince Wigstan of Mercia. Harbard causes a stir with the women of Kattegat.
After facing defeat on the river, Ragnar refuses to retreat, prompting him to change his methods of attacking Paris. Count Odo's plot against Charles and Rollo backfires. Ecbert now rules Mercia, which dissatisfies Kwenthrith.
The Great Army is gathering in Kattegat, as Lagertha is saved by Bjorn Ironside from the hands of Ragnar's sons. Rollo is establishing the kingdom of Normandie as a safe-heaven for all vikings in search for land.