Reward: 500 Renown, 7000 Gold.
Theresa is waiting for you in Gray House. You'll get some more in-depth information about your family's history from her and find out that Jack of Blades is apparently the one to blame. You have to find the Archaeologist again. Go to the Guild and take the Quest Card.
You'll begin this mission north of Bowerstone. You'll have to cut your way through Bowerstone Jail, Windmill Hill, Gibet Woods and Prison Path, facing a new type of enemies, the infamous Minions. You'll have to be quick once you enter Prison Path. Don't fight anyone, just run to the Archaeologist (he's at the end of the path, at the pier) and kill the Minions there. The Archaeologist will be free and he will gratefully tell you about a secret passage to Bargate Prison.