Full spoilers for this episode.
Ragnar's return from Lindisfarne brings treasure and captives to Kattegat, but Earl Haraldson quickly takes control of the reward. He claims the plunder and allows each raider to keep only one item. Ragnar chooses Athelstan rather than gold. Rollo resents his brother's submission, but Ragnar believes resistance would give the Earl an excuse to kill them. The successful voyage has proved that western lands exist without freeing the crew from Haraldson's rule.
At the farm, Athelstan becomes the person Ragnar questions about England, its kingdoms and its faith. The monk refuses an invitation to join Ragnar and Lagertha in bed, holding to his vows despite his captivity. His knowledge gives Ragnar another destination to propose. Meanwhile, Haraldson hides treasure for his afterlife and has a boy killed to guard it, as the drama shows how far he will go to secure his wealth.
Ragnar wins permission for another raid by promising Haraldson its profits, but the Earl requires Knut to accompany him and watch his interests. This time Lagertha goes too. Ragnar leaves Athelstan responsible for the farm and children, angering Bjorn, who objects to a captive being placed above him. The crew reaches Northumbria again, where a meeting with the local sheriff and his men turns violent instead of leading to a peaceful introduction to the king.