Vikings follows the adventures of Ragnar Lothbrok the greatest hero of his age. The series tells the sagas of Ragnar's band of Viking brothers and his family, as he rises to become King of the Viking tribes. As well as being a fearless warrior, Ragnar embodies the Norse traditions of devotion to the gods, legend has it that he was a direct descendant of Odin, the god of war and warriors.
Entry to Valhalla eludes Ragnar but as he lies in his sick bed in Kattegat events unfold beyond his control. Bjorn orders the arrest of Floki for Athelstan's murder while in Paris, Rollo betrays the last of his Viking supporters to strengthen his position in the French Court.
As Ragnar and Floki remain at odds in Kattegat, Rollo makes great efforts in Paris to win over his new bride, Princess Gisla. Bjorn's survival skills are put to the test in the wilderness, while King Ecbert sets the task for his son Aethelwulf to rescue Queen Kwenthrith from opposing forces in Mercia.
Ragnar tells Floki of a heavy price he has paid for his actions but as Floki remains a prisoner, a mysterious visitor to Ragnar counsels mercy. Intrigue prevails at the French Court as Rollo finds an unlikely ally in Count Odo, but can't escape the contempt of his new bride.
The Yule Log burns in the Great Hall in Kattegat and, though Floki must remain out in the cold, other visitors are welcomed, among them a Norwegian King and Bjorn, with a new partner we've met before. King Aelle visits Wessex for Christmas and is not impressed with how family relations are developing.
There's an air of betrayal at Court in Paris and Wessex as those whom Odo trusts plot against him and Ecbert agrees to support Kwenthrith in Mercia, but is Ecbert a true ally? Ragnar confides in Yidu his darkest secret. Pregnancy brings happiness to Lagertha and Kalf and a marriage is arranged, but events on the wedding day take an unexpected turn.
Ragnar announces another raid on Paris at the Thing in Kattegat and although the fleet is battered by a storm after it sets-out, the greatest challenge for the Vikings lies ahead in Paris, where Rollo awaits. Ecbert also has a journey in mind as he dispatches Aethelwulf and Alfred on a pilgrimage to Rome.
In England, King Ecbert's ambitions are revealed as he schemes to gain the crown of Mercia while outside Paris, the Vikings attack with considerable force but can they breach Rollo's defenses? Meanwhile, Harbard, the mysterious wanderer, returns and causes a stir amongst the women of Kattegat.
Defeat for the Vikings calls Ragnar's leadership into question as they evacuate their camp and move back down-river. Ragnar himself remains inscrutable until he orders the fleet to beach at a cliff face and unveils an ingenious plan. Rollo and Gisla have news that strengthens Rollo's position at the French Court whilst Count Odo fails to identify his true enemies, with fatal consequences.
The labors of the Vikings eventually bear fruit as, within sight of Paris, they re-launch their boats but this time along with some interesting structures that Floki has made. Aethelwulf and Alfred eventually arrive in Rome and honors are conferred by Pope Leo but relations are not so cordial in Wessex between King Ecbert and the disgruntled King Aelle.
A ferocious battle between the Vikings and the French eventually comes down to Ragnar against Rollo and the outcome seals the fates of the two brothers.