"A Good Treason" is the first episode of the fourth season of Vikings. It is the thirtieth episode of the series overall. It first aired on February 18, 2016. It was written by creator Michael Hirst and directed by Ciarán Donnelly.
As Ragnar lies in his sick bed in Kattegat, events unfold beyond his control; Bjorn orders the arrest of Floki for Athelstan's murder; Rollo betrays his Viking supporters to strengthen his position; Kalf announces joint Earldom with Lagertha.
The episode opens with Ragnar, wounded and near-death, having a fever dream of walking towards the welcoming open gates of Valhalla, only to see them close before him. The scene was intercut with his loving wife Aslaug asking The Seer if a woman would rule Kattegat should the king Ragnar die.
In Kattegat, Queen Aslaug rules imperiously in Ragnar’s stead, with a returning Bjorn at her side. No sooner have the spoils of Paris been laid at their feet, than Bjorn has Floki arrested for the killing Athelstan. When Ragnar finally stirs, hobbling into a celebratory feast with the help of a wooden staff, he chastises Bjorn for publically shackling up his once beloved shipbuilder turned traitor. Bjorn decides that he will prove to his father that he can live as the great heroes did; he’s going into the interior, to survive deep in the wilderness. Meanwhile, Aslaug procures new slave girl, Yidu, most likely to use as a weapon against Ragnar.
In Hedeby, Earl Kalf announces to his people that he and Lagertha will share the Earldom. This doesn’t go down well with Einar, who helped Kalf get rid of Lagertha in the first place. Kalf invites Einar and his men around a central post so they can vote to exile Lagertha. Then he sneers smugly as his men to shoot all the dissidents down with their shiny new Frankish crossbows. Lagertha expresses her pleasure with a stealy smile, and delivers the final insult to injury, castrating the dying Einar.
In Paris, Count Rollo is settling in to his new life of Frankish nobility. He’s married away to Princess Gisla, who weeps through the ceremony and holds a knife to his throat on their wedding night. “You’re tickling me,” he jokes, before taunting her by falling asleep. Rollo receives a visit from Eirik. It seems the Vikings left behind with him don’t think much of their nominal leader, who’s become a Frankish noble and a Christian. He rides to the Viking encampment outside Paris, gives the signal, and a horde of hidden Frankish crossbowmen cut down every man, woman, and child. With his dying breath, Eirik curses Rollo and promises that Ragnar will avenge them.
- Travis Fimmel as King Ragnar
- Katheryn Winnick as Lagertha/Earl Ingstad
- Clive Standen as Duke Rollo
- Gustaf Skarsgård as Floki
- Alexander Ludwig as Bjorn
- Alyssa Sutherland as Queen Aslaug
- Ben Robson as Kalf
- Lothaire Bluteau as Emperor Charles
- John Kavanagh as The Seer
- George Blagden as Athelstan
- Dianne Doan as Yidu
- Maude Hirst as Helga
- Owen Roe as Count Odo
- Edvin Endre as Erlendur
- Georgia Hirst as Torvi
- Søren Pilmark as Stender
- Morgane Polanski as Princess Gisla
Additional Cast (in order of appearance)
- Stephen Rockett as Hvitserk
- Luke Shanahan as Ubbe
- Elijah O'Sullivan as Sigurd
- James Quinn Markey as Ivar
- Steve Wall as Einar
- Shashi Rami as Slave Trader
- Rosalie Connerty as Angrboda
- Barry McGovern as French Archbishop
- Frankie McCafferty Sinric
- Huw Parmenter as Roland
- Karen Hassan as Therese
- Simon Jewell as Frankish Officer
- Cillian O'Sullivan as Eirik
- Ross Magee as Boat Captain
- Unknown Baby Actress as Siggy