Legendary Viking Duke Rollo arrives, causing further upheaval in a Kattegat still reeling from Ivar the Boneless becoming its king; Floki battles the elements in Iceland, and his own settlers' desire for revenge, to forge a colony.
Ivar the Boneless and King Harald march into Kattegat where Ivar announces that he's the new King. They have a celebration but Ivar says that his revenge won't be complete until Lagertha is dead. Despite having gained everything, Harald is still mourning the loss of Astrid and his unborn child. Ivar points out that there are plenty of beautiful women here that he can move on with and notices that one of them is the slave that he freed, Freydis. In the new colony, Floki suggests that they sacrifice him in order to regain the favor of the gods. He puts it to a vote. Eyvind wants to sacrifice Floki because he believes that he mislead them. Most of the colony agrees. The next morning in Kattegat, Rollo arrives. Ivar thanks him for supporting them in Kattegat Civil War. Rollo says that he did so because he seeks to make an alliance with Kattegat since it is an important trading station. Harald is suspicious and believes that Rollo wishes to rule Kattegat. Rollo puts him at ease and tells him that he rules over enough cities and settlements to satisfy any man. No, Rollo wishes to make a trade agreement and have them agree to send troops if he's ever in need.
The voting is equal but one person hasn't voted yet. It's Eyvind's son and he votes for Floki not to sacrifice himself. Rollo, Ivar, Hvitserk, and Harald share a drink. Rollo admits that he's no longer allowed to fight because he is too important. Hvitserk tells them how Ubbe spared his life while Harald admits to having killed Halfdan. Rollo asks about Bjorn and if he's still alive but then he laughs and says, of course, he is because who could kill Bjorn Ironside. Ivar is still upset about Lagertha and Harald says that they have scouts out looking for them. Rollo wishes them luck in their hunt. Bjorn, Torvi, Ubbe, Lagertha, and Heahmund discuss where they can go where Ivar can't find them. Heahmund suggests that they go to England and ask King Aethelwulf to intercede on their behalf. Lagertha doesn't want to leave her country but agrees to go to England. Torvi brings food to a chained up Margrethe who asks to see Ubbe. Torvi sees Ubbe and motions for him to speak with her. He tells Margrethe that she is too dangerous to be set free. Ubbe says that they can't bring her with them to England. Lagertha asks Heahmund if he wants to return to England and Heahmund says yes. He tells Lagertha that if they do return he won't be able to openly be with her because of his faith. But still, he can't give her up.
Having left in the early morning to find them, Rollo arrives at Lagertha and Bjorn's camp. In Wessex, King Alfred says that they are still gravely threatened by the Northman and that he wishes to increase their defenses. He also wishes for monasteries and churches in his realm to teach prayers and lessons in English to give education and opportunity to the ordinary Saxon folk. The church isn't too happy about this and claims that Alfred has no jurisdiction over them. Alfred stands firm on his decision. He also reveals that Danish vikings have sailed up river and now threaten Winchester. Alfred appoints Aethelred to command an army to defeat them. Lagertha asks Rollo why he has come. Rollo says to save Lagertha and Bjorn by giving them safe passage back to Francia. Lagertha says that it doesn't make any sense. Rollo says he offers her this because he has always loved her and because Bjorn is his son. Lagertha doesn't deny this as Bjorn walks up to them. Lagertha walks away leaving Rollo to explain to Bjorn that he's his father. Bjorn says that he's heard rumors but that he resembles Ragnar more in spirit and principle. Rollo begs Bjorn to allow him to help him and that his life in Francia would be sweet. Bjorn says that he made his choice when Rollo choose to stand with Ivar.
Bjorn tells Lagertha that he's going to kill Rollo because he betrayed them - twice. Rollo begs Heahmund for his blessing for his sins. Bjorn says that he is going to kill Rollo and grabs his axe. Rollo kneels before him and tells both Ubbe and Lagertha to let Bjorn do what he will. Bjorn tells Rollo that he isn't worth it as Lagertha refuses Rollo's offer. Rollo tells Lagertha that they will never meet again as he walks away. Back at Kattegat, Ivar asks Rollo if he found Lagertha and Bjorn. Rollo says he'll tell him where they are but first they must make a deal. Ivar says that he asks for a high price but Rollo points out that he is in a position to do so. Ivar and a group of them go to investigate the camp but find that Bjorn and Lagertha have gone but they have left behind Margrethe. Bjorn and the others sneak through Kattegat and steal a boat as they head to England. Alfred fears that he has already isolated the church. Judith tells him to produce heirs to secure his rule. Alfred asks who he shall marry and Judith says that she'll find him a suitable bride. In Winchester, Aethelred and his army have held back the Danishmen.
Ivar returns to Kattegat with Margrethe. Hvitserk takes her into his care. Heahmund tells Lagertha that he won't betray them because he loves Lagertha. Freydis goes to visit Ivar. She tells him that the Gods have marked him and that he is favored above all men. Ivar tells her that he is in daily danger of being killed. Freydis asks by who and Ivar asks if he can speak openly with her. Freydis says that he can trust her and that she'd give her life for him if he asked her to. She asks him what he would like her to do. Lagertha and the rest of them arrive in England but are surrounded by soldiers. Heahmund asks Aethelred to take them to see King Aethelwulf but Aethelred informs him that he's dead and that Alfred reigns now. Heahmund and Aethelred arrive at the castle with the Vikings being carried in a cage.
- Katheryn Winnick as Queen Lagertha
- Gustaf Skarsgård as Floki
- Alexander Ludwig as Prince Bjorn "Ironside"
- Peter Franzén as King Harald "Finehair"
- Alex Høgh as Prince Ivar the Boneless
- Marco Ilsø as Prince Hvitserk
- Jordan Patrick Smith as Prince Ubbe
- Jonathan Rhys Meyers as Bishop Heahmund
Special Appearance By
- Adam Copeland as Kjetill "Flatnose"
- Kris Holden-Reid as Eyvind
- Ida Marie Nielsen as Margrethe
- Ferdia Walsh-Peelo as Alfred
- Georgia Hirst as Torvi
- Jennie Jacques as Queen Judith
Aditional Cast (in order of appearance)
- Mark Lavery as Ivar's Male Slave
- Alicia Agneson as Freydis
- Leah McNamara as Aud
- Jack McEvoy as Helgi the Lean
- Mei Bignall as Thorunn
- Kelly Campbell as Ingvild
- Elijah Rowen as Asbjorn
- Scott Graham as Frodi
- Lulubelle Earley as Jorunn
- Ryan Henson as Hali
- Svea Killoran as Asa
- Jonathan Delaney Tynan as Lord Cuthred
- Darren Cahill as Aethelred