"The Usurper" is the fifth episode of the third season of Vikings. It is the twenty-fourth episode of the series overall. It first aired on March 19, 2015. It was written by creator Michael Hirst and directed by Helen Shaver.
The fleet returns to Kattegat to find tragic circumstances await. Lagertha learns that her Earldom has been usurped and convinces Ragnar to travel to Hederby with her in an effort to reclaim her title. Ragnar causes great surprise when he announces the next raid. The Seer has interesting prophecies for Rollo.
The Vikings return to Kattegat, and the women learn of Torstein's death as the men learn of Siggy's. Ragnar is suspicious of why Siggy was watching the children instead of Aslaug.
Floki becomes even more outspoken about his anger against Christians, and against Athelstan. Helga tells Floki about Harbard, and Floki claims that Harbard is a god.
Aethelwulf learns that Judith is with Athelstan’s child. He is then sent by King Ecbert to the Northmen's settlement to quash issues between settlers and Christians after the Christians burned down one of the houses of the Northmen.
A messenger arrives in Kattegat to tell Lagertha that her earl-ship has been usurped by Kalf. She asks Ragnar to assist her in retrieving her position. Ragnar tells the men that they will raid and conquer Paris in the spring.
Ragnar accompanies Lagertha to speak with Kalf, although he decides to not help fight for Lagertha's earl-dom. Instead, Ragnar asks Kalf if he would join the raid on Paris.
Aethelwulf leads a group of soldiers to the Northmen settlement, but instead of peace, decides instead to kill them.
Floki tells Ragnar that Aslaug slept with Harbard and tells him that Harbard was simply another name for Odin.
King Ecbert finds out that the nobles and his son, Aethelwulf, killed the settlers. Ecbert asks to speak privately with his son, where he reveals that it was his plan from the beginning to slaughter the settlers and never wanted to allow the Northmen to settle on his land.
- Travis Fimmel as King Ragnar
- Katheryn Winnick as Lagertha/Earl Ingstad
- Clive Standen as Rollo
- Gustaf Skarsgård as Floki
- George Blagden as Athelstan
- Alexander Ludwig as Bjorn
- Alyssa Sutherland as Queen Aslaug
- Ben Robson as Earl Kalf
- Linus Roache as King Ecbert
- Moe Dunford as Prince Aethelwulf
- Maude Hirst as Helga
- Gaia Weiss as Þorunn
- Jennie Jacques as Princess Judith
- John Kavanagh as The Seer
Additional Cast (in order of appearance)
- Michael Hough as Warrior 2
- Jack Hickey as Warrior 3
- Ciarán McGlynn as Saxon 2 Farmstead
- Marty Maguire as Second Saxon Noble
- Muiris Crowley as Third Saxon Noble
- Jill Harding as Judith's Maid
- Cathál Ó'Hallin as Hvitserk
- Cormac Melia as Ubbe
- Steve Wall as Einar
- Unknown Baby Actor as Ivar