This quest begins after completing Arrive Unexpected. Soma has agreed to help Eivor destroy Fulke’s supplies in Crawleah. You’ll need to meet her there to begin.
You will find Soma just west of Crawleah, waiting in the bushes. When you speak with her, Soma will give you the option of charging into the town in a battle frenzy, or using archers instead from afar instead. Whatever you choose, you will need to go inside the town to burn it. The only difference is that if you choose to use archers, there will be fewer bodies running around the town as you burn it.
Unlike in Guildford, your allies will help you to burn houses and supply carts here. All you need to do is run through the town, killing Saxon soldiers and bandits, while helping your allies by throwing torches at the supply carts and houses. You’ll need to keep burning until the progress bar is completely filled, at which point the quest will end.