Spoilers for this episode.
Ragnar sails back to Wessex as a king, bringing settlers as well as warriors to claim the farmland promised by Ecbert. Lagertha wants a place where her people can grow crops, but Ecbert attaches a military obligation to that hope. Ragnar must fight for Princess Kwenthrith in Mercia, where her uncle and brother oppose her claim. The settlement and the campaign become parts of the same bargain.
Before leaving, Lagertha asks the Seer about her future and receives a warning about betrayal. She leaves Kalf in charge at Hedeby, unaware that he is discussing a move against her with Einar. In England, Ecbert takes an interest in Lagertha while Athelstan helps the visitors communicate with their hosts. Bjorn brings Porunn into the expedition, although her wish to fight unsettles his hopes of keeping her safe.
The opposing Mercian armies wait on different sides of a river. Ragnar concentrates his attack on Kwenthrith's uncle rather than dividing his own force between both enemies. The Vikings overwhelm that army while her brother Burgred watches from the other bank, unable to save his uncle. Ragnar has won the first battle of another ruler's war, but Burgred remains beyond his reach and the promised farming life still depends on fulfilling Ecbert's terms.