Full episode spoilers.
The defeated Vikings begin withdrawing along the river, and Bjorn challenges Ragnar over his leadership. Ragnar finds another route when he spots cliffs beside the water: the fleet can bypass Rollo's forts by moving overland. He asks Floki to make the equipment, and the shipbuilder helps devise the lifts and rollers. Their work raises the longships out of the river and gives the expedition a way to continue toward Paris.
Ragnar's renewed planning does not end his dependence on Yidu's supply. Their argument turns to her freedom and his demands, and he drowns her in front of Ubbe and Hvitserk. In Kattegat, Sigurd shows Aslaug that Harbard has been sleeping with other women. She confronts him and rejects his excuses. In Paris, Therese lures Odo into a trap, where Roland whips him to death under Charles's authority, removing a rival to Rollo.
Ecbert returns to Wessex having secured Mercia for himself. Kwenthrith learns that she will not regain her throne, despite his promises, and reveals that she is carrying Aethelwulf's child. Her attempt to escape fails, leaving her trapped at court without the kingdom she expected. She then enters Ecbert's room to kill him. Judith intervenes and stabs Kwenthrith, saving Ecbert but leaving the queen dead and confronting him over what their relationship has made her do.