Season synopsis
Contains spoilers for this season and earlier seasons.
Rollo fights for Jarl Borg against Ragnar, then surrenders rather than kill his brother. Ragnar brokers a truce and secretly pays for Rollo’s release. At home, Aslaug arrives pregnant, and Ragnar’s wish to keep both women drives Lagertha away with Bjorn. Four years later, Ragnar and Horik sail to Wessex after excluding Borg from their alliance. Borg retaliates by occupying Kattegat, forcing Rollo to hide Aslaug and the children until Ragnar can return.
Lagertha brings reinforcements, and Ragnar’s attack drives Borg out. She returns to her abusive husband Sigvard, stabs him in the eye, and becomes earl after Einar kills him. Ragnar later captures Borg under the pretense of renewing their alliance and executes him by the blood eagle. In Wessex, Ecbert saves Athelstan from crucifixion and makes use of his learning. After defeating the Vikings, Ecbert offers them farmland and work as mercenaries. Aslaug also gives birth to Ivar, whose disability makes Ragnar question whether he should live; she insists on keeping him.
Horik tries to recruit Floki and Siggy into a plan to murder Ragnar’s family. Floki appears to poison Torstein to prove his loyalty, while Siggy is told to kill the children. When Horik launches his attack, both supposed allies remain loyal to Ragnar, and Torstein is revealed to be alive. The trap turns against Horik, whom Ragnar kills. Ragnar spares Horik’s son Erlendur and emerges as king, with the English settlement still a promise rather than an established home.