Farmer, family man and rebel Ragnar Lothbrok is determined to sail west to discover new lands and riches despite an intimidating warning from his village's tyrannical leader, Lord Haraldson, who makes it clear in no uncertain terms that doing so could result in severe consequences.

Ragnar and his crew return from their trip with treasure, and Earl Haraldson has no choice but to sanction another raid. The west is open for the taking, and the Vikings' world will never be the same.

A seer reads Earl Haraldson's future and tells him that Ragnar searches for his death.

Three Viking ships sail toward the Royal Villa of King Aelle in eastern England. Ragnar wants ransom in exchange for peace, but the king has a very different plan in mind.

Ragnar travels to Götaland to help King Horik resolve a land dispute with the area's leader, Jarl Borg. Meanwhile, sickness infects the village of Kattegat, and the people look to Lagertha to help them appease the gods.

The battle begins between Ragnar and King Horik's forces against Jarl Borg; Princess Aslaug makes her way to Kattegat.

King Ecbert finds himself facing an entirely new kind of foe; Ragnar races to dominate in the west; Jarl Borg has his own plans in store for the future of Kattegat.

Lagertha and Ragnar unite to try to win Kattegat back from Jarl Borg; Aslaug must face the truth of her prophecies; Athelstan struggles to define his faith; Bjorn must once again make a choice.

Ragnar and King Horik clash over how to dispense justice to Jarl Borg. In Wessex, King Aelle arrives and Ecbert has an eye on a new alliance.

Ragnar's warriors march on to King Ecbert's villa and are met with a surprisingly vicious welcome party.

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.

King Ecbert visits the developing Viking settlement as the first harvest is sown.

The fleet returns to Kattegat to discover tragic circumstances await.

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.

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.