How to unlock: After saving Nick Valentine during the Unlikely Valentine quest you must visit his detective agency in Diamond City (M6,1) and check the investigation files of Marty Bullfinch and listen to holotape.
- Find the Gilded Grasshopper
- Read the "Food for the grasshopper"
- Find the grave of Shem Drowne
Unlock the investigation
You can start this quest after saving Nick Valentine during the main storyline of the game. Once you do it, go back to Diamond City Market and go to Valentine Detective Agency. Find Marty Bullfinch Case File after walking into the building. It is lying on one of the file lockers. Taking the files will also give you Marty Bullfinch's Holotape. Open the inventory, find the tape and listen to it. Now the quest will start and will be added to your journal.
Important - During this quest you don't have to travel with Nick, but if you take him with you, you will hear many of his comments.
Find the Gilded Grasshopper
Leave the market and go to Faneuil Hall location that can be found east from your current position. This territory is occupied by strong supermutants and you will meet them both in front of the building and inside it, where your destination is. Keep going up through the Faneuil Hall, you must reach the ladder that neighbors the hatch leading to the roof.
Once you reach the roof, you can examine the corpse of Marty Bullfinch. However, it is more important to take the Gilded Grasshopper shown on the picture above. Open the inventory, find the Food for the Grasshopper note and read it.
Find the grave of Shem Drowne
Go back down and leave the building (or simply use the quick travel). The grave that you seek is located north from Faneuil Hall, near Pickman Gallery and Old North Church (in which Railroad faction has its HQ). Find the small cemetery, get rid of the ghouls and locate the correct grave. The quest will end when you will open the coffin. It is a good idea to take Shem Drowne Sword which is a unique artifact (in addition to that, you will also find the note in the coffin).
Quest rewards: Experience points, Shem Drowne Sword.