"On the Eve" is the nineteenth episode of the fourth season of Vikings. It is the forty-eighth episode of the series overall. It first aired on January 25, 2017. It was written by creator Michael Hirst and directed by Ben Bolt.
The Viking army causes panic in the English countryside as King Ecbert and Aethelwulf plan the defense of the realm. Kattegat is put under siege by Egil. Bjorn and Ivar fight over control of the Great Heathen Army.
Kattegat is attacked by Egil and his men, but they are repulsed and Egil is captured, Torvi is injured while defending the city. Under torture, Egil confesses to Lagertha that he had been paid by King Harald to attack her. Meanwhile in Mercia, terrified villagers flee before the advancing heathen army. Harald pretends to forgive Ellisif, then kills her husband Vik. Ellisif later pretends to forgive Harald, seduces him, and is about to kill him but is killed herself by Halfdan. Aethelwulf gathers a large army in Wessex and moves to intercept the advancing vikings. Before they meet, Ivar persuades Bjorn to scout a potential battlefield and plan to use the terrain to defeat the Saxons. The following day, the vikings surprise the Saxons by ambushing them from the woods on each side of the battlefield, until they have them surrounded near Repton.
- Katheryn Winnick as Lagertha
- Gustaf Skarsgård as Floki
- Alexander Ludwig as Bjorn
- Peter Franzén as King Harald "Finehair"
- Jasper Pääkkönen as Halfdan "The Black"
- Moe Dunford as Aethelwulf
- Alex Høgh as Ivar
- Marco Ilsø as Hvitserk
- David Lindström as Sigurd
- Jordan Patrick Smith as Ubbe
- Linus Roache as King Ecbert
- Josefin Asplund as Astrid
- Maude Hirst as Helga
- Ida Marie Nielsen as Margrethe
- Georgia Hirst as Torvi
- Jennie Jacques as Judith
Additional Cast (in order of appearance)
- Connor Lambert as Viking Trader
- Gary Murphy as Bishop Unwan
- Rob Walsh as Aelle's Cleric
- Phillip O'Sullivan as Bishop Edmund
- Isaac O'Sullivan as Alfred
- Unamed credited actor as Aethelred
- Olga Wehrly as Saxon Woman
- Lee Hunter as Saxon Scout
- Sinead Gormally as Tanaruz
- Adam Goodwin as Saxon Noble
- Charlie Kelly as Egil
- Sophie Vavasseur as Princess Ellisif
- Gary Buckley as Vik (Ellisif's Husband)
- Siobhan Kelly as Egil's wife
- Peter Dillon as Viking Scout
- This episode marks the death of Bishop Unwan - advisor of King Aelle - as well as the death of Princess Ellisif and her husband Vik. Egil died off-screen from his wounds or executed.