The season opens with Ragnar returning to Kattegat from Paris, badly wounded and hallucinating, while a power vacuum begins to form in his absence.

While Ragnar recovers, Bjorn takes on a more prominent leadership role, even arresting Floki for the murder of Athelstan—a move Ragnar initially disapproves of because it was done so publicly.

This half also introduces Yidu, a slave who becomes Ragnar's confidante. Their relationship is centered around a "medicine"—likely a mix of opium and psychedelics—that fuels Ragnar's growing addiction and withdrawal from his family. Part 2: The Death of a Legend Vikings Season 4 Review - Keith Loves Movies

The fourth season of Vikings is often described by viewers as a massive, "Hollywood scale" expansion that officially marks the end of an era for the show's "old guard" and the rise of a new generation. Doubling its usual length to 20 episodes, the season is split into two distinct halves that chronicle the fall of Ragnar Lothbrok and the vengeful emergence of his sons.