Full spoilers for this episode.
Ragnar decides to travel to Uppsala after Lagertha's miscarriage, asking why the gods have given him power while taking away his unborn child. Lagertha wants another son too, and the family joins the journey with Athelstan and their companions. At the temple, prayers and celebration surround preparations for sacrifice. Athelstan sees animals being gathered in groups of nine and learns that people have also been chosen to die during the festival.
The gathering gives Ragnar an opportunity to meet King Horik and offer him allegiance. He asks for help sending larger raiding parties west, including toward Francia, a place Athelstan knows from his earlier travels. Horik accepts his service and asks him to represent the king in a dispute with Jarl Borg over land. Away from their meeting, Siggy presses Rollo to take his ambitions seriously instead of letting drink and resentment keep him outside his brother's growing circle.
Athelstan is brought before a priest and discovers that Ragnar intended him as a human offering. He denies still being Christian, but the priest concludes that he has not abandoned his faith and is neither willing nor acceptable to Odin. The group must provide someone else. Leif volunteers to die for his family, friends and the people of Midgard, and the ceremony proceeds. Athelstan survives, having learned that his place in Ragnar's household has not protected him from being offered up.