While Ragnar must deal with the aftermath of the fatal storm, Bjorn goes to meet his uncle. Meanwhile, Lagertha returns to Kattegat.
While the great and the good descend into Kattegat in preparations for Bjorn Ironside's voyage to Rome, Ragnar must try to convince the remainder to join his raiding party to England.
In the 10th episode (mid-season finale), victory proves costly in the battle between the Vikings and the French as Ragnar squares off against Rollo, sealing the fates of the two brothers.
As they near Paris, the Vikings relaunch their boats, but this time they bear interesting structures made by Floki; Aethelwulf and Alfred arrive in Rome, where honors are bestowed by Pope Leo IV, but in Wessex, relations are less than cordial between King Ecbert and a disgruntled King Aelle.moreless
Ragnar launches the attack towards Paris. Rollo is however prepared for his fellow Vikings. In Wessex, King Ecbert sets out to meet Prince Wigstan who then gives an tempting offer to the King. In Kattegatt, Harbard meets the women of the village.moreless
It's Christmas time. Ragnar spends some alone time with the new slave Yidu. Bjorn has an unexpected encounter in the forest. Ragnar come home to find his chair in the great hall occupied by another king.moreless
Both Ragnar and King Ecbert gets a visit by Athelstan. Aethelwulf comes home after a successful rescue mission. Rollo tries to learn the language in Paris which proves difficult.
Floki has escaped and the search for him is on. In Wessex the King gets some bad news about his allies. Aethelwulf is off on a rescue misson.
As Ragnar prepares to take his troops for one more daring attack on Paris, he makes a request of his son that could change the future of the Vikings for ever.
As a second assault on Paris is being prepared, Emperor Charles must make a difficult decision. Meanwhile, in Wessex, Judith must make her own difficult choice.
The Viking army attacks Paris as the city musters its forces for defense.
The populace of Paris is in a panic after the appearance of the Viking fleet, and Emperor Charles, at the behest of his daughter, announces he'll remain in the city.
While Rollo worries about the Seer's prophecy, the Vikings make final preparations for their raid on Paris.
Tragic circumstances greet the fleet on its return to Kattegat; Lagertha is usurped and convinces Ragnar to help her reclaim her title.
An alliance angers Floki; Princess Kwenthrith makes political moves.
As the new Viking settlement prepare for their first harvest, King Ecbert pays them a visit.
A mysterious wanderer arrives in Kattegat; Lagertha and Athelstan establish a Viking settlement.