Diamond City Blues

Diamond City Blues is a quest in Fallout 4.

Quick walkthrough
1. Visit the Colonial Taphouse and watch Paul Pembroke get beaten by Henry Cooke. 2. Wait until later and talk to Paul around town to get the quest. 3. (Optional) Demand payment with a speech check. 4. Follow Paul to the Colonial Taphouse to confront Cooke. 5. At this point you have the option to do an easy speech check to get Paul to calm down, or encourage him to attack Cooke. 6a. Encourage Pembroke to kill Cooke, then finish the fight. You can get Cooke's note from his body telling you about a drug deal going down north of town. 6b. Discourage Pembroke from killing Cooke, this results in talking about the chem deal and moving forward much the same from there. 7. Go north to quest marker, don't bother talking to them as all options lead to combat. 8. Once everyone else is dead you can interrogate Trish, there's a few speech checks you can make for extra XP, but it's not hard to get her to give up the details on the chem lab. Alternately can kill her and take a note off her body. Make sure to grab the chems before leaving. 9. Head to Four Leaf fishpacking plant on the East coast, being wary of the ghouls as you approach, and of the tripwires around the building. Climb to the top and make your way to the terminal on the side to gain access to the lab. 10. Once you gain access the quest is considered complete.

Detailed walkthrough
The quest starts in Diamond City where the player character must help Paul Pembroke deal with Henry Cooke, the barkeeper of The Colonial Taphouse, and then intercept a drug deal in order to gain access to a chem lab. The quest is obtained by witnessing Pembroke get in a fight with Cooke over Pembroke's wife. The fight happens when the player character enters The Colonial Taphouse in Diamond City for the first time. Shortly after the scene Paul Pembroke will seek out the player character in Diamond City and the actual quest starts.