Horik and Ragnar agree that additional ships and warriors will be needed if they hope to return to England. Horik persuades Ragnar to delay killing Jarl Borg lest the execution scare off any potential allies. Helga reveals that she is carrying Floki's child and the two agree to finally wed. When Helga wishes to get Ragnar's blessing, Floki claims they do not need it. Ragnar visits the seer who reveals that Athelstan is physically alive but spiritually torn over which path to embrace. In England, King Ecbert proposes an alliance with King Ælla against both the weak English kingdom of Mercia and the expected return of the Viking raiders. To alleviate the hesitant Ælla, Ecbert weds his son to Ælla's daughter, sealing their alliance. Ragnar's call for an ally is answered by a mysterious Earl, who is revealed to be Lagertha. Rollo forces Siggy to admit she is sleeping with Horik. Horik allows Jarl Borg, to the very end, to harbor hope of escaping his fate, but when the jarl emerges into the center of Kattegat, the entire population is in attendance to witness his horific death. Ragnar performs the Blood Eagle on Jarl Borg, who endures the torturous, horrific death without crying out, proving himself worthy of Valhalla.
The title is a reference to the fabled execution method of the Vikings. It was performed by slicing open the back of the victim, then hacking the ribs away from the spine, causing them to spring apart to resemble bloody wings, then drawing the lungs out of victim's back and draping them over the shoulders. Salt was often thrown into the wound. The victim would most likely have died before the process was finished.
Kings Ecbert of Wessex and Aella of Northumbria were not exact contemporaries in real life. Ecbert of Wessex lived from 769 until 839, while Aella lived as late as 867, around the time that the Great Heathen Army invaded Northumbria.
The marriage between Judith and Aethelwulf of Wessex took place in 856 CE, more than fifty years later than depicted in the series. Also, Judith was Aethelwulf's second wife, whom he married many years after becoming king of Wessex. And Judith was a daughter of the Frankish King Charles the Bald, not the Northumbrian King Aella.
The song played during the carving of the blood eagle is "Loeyndomsriss" by Wardruna. The song is part of a larger invocation of Thurses.