Fallout 4 created by Bethesda Game Studios.
Images used for educational purposes only.
Main Walkthrough

Prerequisites: Arrive in Diamond City
Trigger: Visit the Colonial Taphouse
Reward: 80 Bottlecaps, 436 XP

- In order to trigger this quest you first need to visit the Colonial Taphouse, a bar in the Stands of Diamond City. You’ll find it up a set of stairs to the right of the main entrance to Diamond City. Once inside you’ll see a fight between the bartender and a dude named Paul; watch it until Paul leaves.

- Return to Diamond City. At some point while you’re wandering around city central’s stands (it took me about a day for this to trigger, mind) you’ll be approached by Paul. He’ll ask for your help in intimidating the bartender into staying away from his wife. Agree (and, if Charismatic, ask for more than 80 caps) to trigger the quest.

- Head up to the Taphouse. Here you’ll see Paul arguing with Cooke, the bartender. You can either help Paul kill Cookie or try to persuade him to calm down. If you kill him you can search his body for Cooke’s Note (and the Cookie Residence Key, ‘cause why not); if you persuade Paul to calm down, you’ll get into a dialogue. Either way, you’ll learn about a drug deal with someone named Trish. You need to go intercept. 

- Once you’ve talked to Cooke / read the Note, leave Diamond City and head to Back Street Apparel. It’s located north of Diamond City, along the waterfront overlooking the Wreck of the USS Riptide. If you’ve never been here before, expect the area around Back Street Apparel to be absolutely lousy with Raiders, as well as a few Turrets near the entrance. (Here’s an article with details about the inside of Back Street Apparel, if you feel like entering.) If you have been here before, the fast travel option will dump you riiiiight near the drug deal, which is taking place on the waterfront. (Check the pipes behind where you appear for a Missile Launcher.)

- The drug meeting, regardless of who you bring or how it goes down, is a shootout in waiting. You can get around this rather easily by lobbing a grenade into the middle of it and killing everyone before you start talking. Just make sure not to kill Trish, who will surrender once her men are dead. You can then coax the location of a big chem stash out of her… or just kill her, take Trish’s Note, and find out that it’s Four Leaf Fishpacking. Either way. (Trish has a lot of ammo on her, so it’s kinda worth it to finish her off.) Be sure to check Nelson Latimer, the other member of the deal, for a ton of Bottlecaps (837!) and the Latimer Residence Key.

The location of the Four Leaf Fishpacking Plant in Fallout 4.
Four Leaf Fishpacking Plant

- The location of the chem lab, Four Leaf Fishpacking Plant, is found on a stretch of land jutting into the eastern bay, closer to Diamond City than Back Street Apparel.You’re going to wind up wandering through Super Mutant territory almost regardless of how you get there - though be careful if you decide to head east along the riverfront, as there’s a Super Mutant just down the street from Back Street Apparel with a Missile Launcher, watching an overpass. Ow. Perhaps the safest way is to swim there from Hesters Consumer Robotics, a waterfront property almost directly east of Diamond City.

- Have a look around the periphery before trying to infiltrate the Plant. There’s a series of stacked containers just before you hit the fence around the Plant, and if you look through these you’ll find the occasional box of ammo. Once you move past these containers you run an excellent chance of finding a number of Feral Ghouls that will chase you around. Use the containers to create box canyons so these bastards don’t bother you as much. A stealthy approach will help you avoid getting mobbed.

- Slip around to the rear of the Plant (if you go east along the shore you can avoid trouble) you’ll find a hole in the fence. Back here you’ll also find Modified Tripwire traps which you cannot disarm. These Tripwires are part of the quest, and you can go through ‘em without harm. Go up the stairs to the top of the building, minding the Super Mutants in the next building over from this. They might ignore you, but they also might not.

- There are more Ghouls on the roof, most of them clustered around a central point; take advantage of this with an explosive or two. Check a nearby structure for a Fusion Core, and climb the stairs on the smokestack to find an Expert locked safe at the very top of the Plant. There are stairs near the Ghoul campout site, with another Tripwire partway down.

- Head to the west side of the building, back on the ground. There’s a door down here you can use to enter the Plant, again with a Tripwire out front. This is the last of the five Tripwires you need to note. This door does not lead to your destination, so if you want to finish the quest, don’t enter yet.

Marowski's Chems Lab in Fallout 4.
Kinda disappointing, really.
Marowski’s Chems Lab

- Pull out Trish’s Note. It has a picture of the Plant’s exterior, as well as the numbered locations of the five Tripwires. You need to trip each of them in order to open the way to Marowski’s Chems Lab. (Do this at night if you have trouble seeing them - the puzzle will reset if you do them in the wrong order.) Trip them in this order, jumping over Tripwires that you should be skipping if they get in the way:
  • The Tripwire beside the transport truck at the side of the Plant
  • The Tripwire attached to the stairs that lead to the roof of the Plant
  • The Tripwire by the entrance to the Plant
  • The Tripwire attached to the front of the transport truck
  • The Tripwire on the roof
Trip them in this order and a door will appear near the last Tripwire. This is the Chems Lab. (I’m pretty sure you can bypass this by Master hacking the terminal on the roof, by the last Tripwire, but I’m not positive.)

Trish's Note. If you don't have it, for some reason, this should help.
- As soon as you enter the Lab you’ll complete the quest. You’ll also be accosted by a number of Chem Lab Workers who are extraordinarily weak. Pick them off and have a look around. There’s honestly not a ton to see - plenty of Jet, Psycho, RadAway, etc., what you’d expect in a drug lab - and you might be a bit disappointed… until you notice that the Hazmat Suits the dead guys are wearing offers immunity to radiation. Oooo! Grab a suit for yourself.

- Also in this room is a double door with a terminal beside it. Use the terminal to open the door and you can find a path into the Four Leaf Fishpacking Plant, which is an interior area unto itself. We’ll explore it in this article. The door from the Lab opens onto a catwalk that makes exploration of the Plant a bit easier, but not by much.

Aftermath

 Remember all that stuff about Cooke from the beginning of the quest? Nothing comes of it if he's still alive, but if you kill Cooke you may face a confrontation from Colette, his estranged daughter. She'll find you in Diamond City and ask you about her father, and if you admit to killing him (or fail at lying about it) she'll try to kill you. You can talk her down by saying that he was an adulterer, but otherwise, take her out. Yaaaay?

Main Walkthrough