Full episode spoilers.
Bjorn and Harald prepare their defences against Oleg's invasion, but the support they need from Norway's other rulers fails to arrive. Bjorn sends appeals in his own name and takes charge of the battle plans. Ivar studies the terrain with Oleg and considers the river and cliffs as routes around the defenders. Both sides prepare for a fight in which the Rus have far more soldiers.
Gunnhild loses her unborn child while helping with the preparations. Bjorn grieves with her and makes clear that he wanted their son. Harald approaches Ingrid, drawing attention to her position as Bjorn's second wife. When she refuses him, he rapes her. In Kiev, Katia visits Ivar wearing a blonde wig and speaks about the resemblance to Freydis. She also reveals that she knows he helped Dir escape, leaving Ivar unsure how far to trust her.
The Rus attack the shore while another force uses the river and scales the cliffs. Bjorn's defenders roll spiked obstacles down onto the attackers, but their resistance cannot stop the invasion. Harald falls wounded, and Erik leaves with his crown. The fighting is intercut with a quiet conversation between Bjorn and Ivar on the beach about their father and the gods. Bjorn is shown being run through by Ivar's sword. The Rus celebrate their victory, while Bjorn's severe wound leaves his fate unresolved.