The Blades and the Seal
The Blades and the Seal is a side mission offered by Drewn Ansilla in Ansilla's Camp in the Caeled Coast.
He needs two family heirlooms that are locked in a box; the key is with a Gastyr in the Castle Gastyr. Go to Castle Gastyr in the Caeled Coast and locate the marked NPC. She has the "Ansilla Key" and you may pickpocket, persuade, or assist her in getting the key.
Once you have the Ansilla Key, there are two ways to complete your quest. Go to Seawatch where the quest marker tells you and get the items from the chest. Alternatively, you may go to the Shining Labyrinth in the Forsaken Plains
Once you have the contents of the chests, return to Drewn Ansilla (he will relocate to Castle Ansilla if you complete The Lost Squad) and complete the mission.