You will receive this quest at the end of "The Alliance Map" quest after you have decided to form an alliance with the people of Grantebridgescire.
Eivor sets out to find the leader of the Summer Army and form an alliance. The army's last known location was just outside Grantebridge.
Talk to the men camped north of Grantebridge at Duroliponte ruins. One of the men will tell you that the Saxons managed to take the village back and that their leader, Soma, is hiding in the swamps. You decide to find her.
Head to the place marked on the map, you should see a Soma's longship there.
Go ashore, approach the boat and kill the opponents you run into there. Soma is not among the imprisoned, you must look for her.
Go to the nearby settlement - Middeltun, there you will find Soma and you will start talking. She will ask you to help her rescue her three advisors.
Thanks to her, you will also learn the identity of one of the members of the Order - Wigmund. This quest will end and you will receive another.
