Diamond City Blues

Head to the Colonial Taphouse in the upper benches south of the market. Upon entering here the first time around, you'll see an argument between Paul Pembrooke and Henry Cooke. After Paul gets beaten, Henry will talk to you. Now leave the establishment and find Paul walking around town. He'll approach you and ask you to come with him to talk to Paul.

At this point, you can pass a speech check to ask for money but he'll only give you 80 caps for doing so successfully. Then, you have the option to confront Henry alone or go with Paul. After accepting the job, the quest will then start. Follow him back to the bar and once Paul confronts Henry, you'll have the option to calm down or have him attack Cooke instead.

If you prevented Paul from killing Henry, (or didn't kill him if you've gone alone), Henry will offer amends in the form of a drug deal going down north of town. If Paul or you killed Cooke, you can still find out of about this deal by looting the note from Henry's body.

Once done, leave the bar and head to the Back Street Apparel where Lartimer's chem deal will take place. Approach them and kill them all, except for Trish. Interrogate her to learn the location of Marowski's stash in the Four Leaf Fishpacking Plant. Further successful speech checks from her will allow you to learn about the tripwires and even get the password to bypass the tripwires.

Even if you let Trish leave, Cooke (if he's still alive) will attack her. Once killed, you'll have to divide the loot with Paul. He'll state 50-50 but you can pass a speech check to convince him on a 70-30 split.

Once done, Paul will leave and you'll have to go to the real stash in the Four Leaf Fishpacking Plant. If you obtained the password from Trish through interrogation, you can ignore the tripwires and head directly to the rooftop. Find the terminal in the catwalk to the NW and operate it to open the door to the lab right beside it. Enter it and the quest will be complete. You also need to kill the chem lab workers inside before you can freely loot the area.

When you're back in Diamond City and you talked to Malcolm Latimer, he'll confront you for killing his son. You can deny this with a difficult speech check; otherwise, you'll be forced to admit it. If you do, he'll randomly send a couple of Triggermen to kill you. If you engage these, surprisingly the People of Diamond City will treat you as enemies (or this could be a bug that happened to me) so make sure to save often especially if you're visiting the city.