To get to Fort Frostmouth go south from Old Attius Farm, then go east between two rock formations.
Nevertheless, Captain Veleth will ask the player to investigate the fort for the source of these attacks. Veleth will find this note odd as it is from a General Falx Carius, who ruled over Fort Frostmouth some 200 years ago.
On one particular corpse is a letter called 'Declaration of War'. Offer to help him and begin searching the ash piles of the Ash Spawn. He fears they are being controlled, but by what is anyone's guess. He will explain that Ash Spawn have been attacking more frequently and with more organization. Kill the Ash Spawn and talk to Captain Veleth afterwards. Assist Captain Veleth against several Ash Spawn. Head straight ahead to the Old Attius Farm. Begin heading east from the harbor in Raven Rock through the gate.