Full episode spoilers.
Ragnar's renewed attack on Paris meets defences planned by Rollo. The Viking ships advance along the river while Lagertha leads an attack on land, but the Franks hold their positions. A chain stretched across the water catches the fleet, throwing men overboard and exposing the ships to fire. Ragnar dives in to save Floki, and Bjorn helps organise the retreat as the assault collapses around them.
The returning Vikings discover that Frankish troops have also attacked their camp. Torvi and Ragnar's young sons survive by hiding, while Helga is badly burned. Ragnar shouts at Rollo over the betrayal, reminding him that he once protected his brother when others wanted him dead. Days pass without a new plan, and Bjorn confronts his father. Ragnar turns back to Yidu, demanding more of the substance she has been giving him.
In Kattegat, Aslaug welcomes Harbard's attention while Sigurd watches their behaviour. Floki experiences a vision of being with Aslaug that shifts into an image of Harbard, connecting his experience to events far from the defeated fleet. In England, Ecbert meets a Mercian prince who offers to surrender the kingdom in exchange for help against its ruling council. The offer would give Ecbert Mercia rather than restore Kwenthrith to the throne he promised her. Back in his tent, Ragnar tells a severed head that they will retreat tomorrow.