In of Vikings , titled " Revenge ," the sons of Ragnar Lothbrok finally unleash the Great Heathen Army upon England to avenge their father's death. Key Plot Highlights

After much tension between Bjorn Ironside and Ivar the Boneless regarding who should lead, the massive Viking force lands on the coast of Northumbria.

The Vikings easily overrun the meager forces of King Aelle . In one of the series' most brutal sequences, the brothers capture Aelle and subject him to the "Blood Eagle" execution at the site where Ragnar died.

Ubbe and Margrethe marry, but Ubbe agrees to share his bride with his brother Hvitserk. Meanwhile, King Harald encounters Princess Ellisif, the woman for whom he sought to conquer all of Norway, only to find she has married another. Production Context Vikings recap: Season 4, Episode 18 - Entertainment Weekly

Prince Aethelwulf confronts his father, King Ecbert , about his lack of affection and his affair with Aethelwulf’s wife, Judith. Ecbert ultimately asks his son to lead the defense against the impending Viking invasion.

Back in Kattegat, Lagertha performs a human sacrifice of Earl Jorgensen to ensure the gods' favor for the army in England.