Tradecraft

Tradecraft is a quest and achievement/trophy in Fallout 4.

Quick walkthrough

 * 1) Talk with Deacon.
 * 2) Meet Deacon at the Old Highway.
 * 3) Follow Deacon and find "The Tourist".
 * 4) Talk to Deacon.
 * 5) Get inside the escape tunnel.
 * 6) (Optional) Enter base through main entrance.
 * 7) Get Carrington's prototype.
 * 8) Leave The Switchboard.
 * 9) Meet Deacon at the Old North Church.
 * 10) Talk to Desdemona.
 * 11) Follow Desdemona.

Detailed walkthrough

 * 1) Talk to Deacon about things that need to be done; you can pass a set of 3 persuasion checks of increasing difficulty to find out that he's had his eye on you already.
 * 2) If you accept the job, Deacon asks you to meet him at the old highway. The marker is roughly between Drumlin Diner and Rocky Narrows Park.
 * 3) Deacon is found wearing "wastelander camouflage" - talk to him a bit and then head off on the mission.  Along the way you'll get some info on "Rail signs"; directions given by the Railroad through graffiti.  There will be ghouls on the way.
 * 4) Once you reach the "tourist," give him the password and get the recon report from him, then talk to Deacon again.
 * 5) You'll be given the choice of a frontal assault or going in through the old escape tunnel.

Option 1: Escape tunnel

 * 1) Go back to where you met Deacon and then head for the quest marker. If you haven't picked it up yet, there's a suit of power armor on the train you go past, requiring an Advanced terminal hack.
 * 2) Once you enter the tunnel, you're given a little more information about the Railroad and the target.  Shortly after the talk, you'll find a Master level terminal which you have to hack to lift the security lockdown and proceed. Deacon will unlock this for you.
 * 3) Once past, Deacon will point out a railsign signifying that there's a cache nearby. It's in the back of the tube directly behind the sign.  Around here, Deacon will warn you to just run if you meet a Courser, provided the player hasn't previously fought one in the Hunter/Hunted quest.
 * 4) Ahead, there will be an unlocked terminal which you can use to turn off the spotlights and turrets.
 * 5) Once past that group, you'll be given a chance to turn on some defenses that will give you an edge against the next group of enemies. Shortly after that, you find out that the Railroad was using an old DIA site as their HQ.
 * 6) Next to the door leading out of the office area you go through, there's a terminal you can use to turn off the tripwires in the next room.  Before leaving, grab the fusion core in the room left of where you first entered and a Covert Operations Manual on a desk in the room up the stairs.
 * 7) If you go right, there's some bathrooms with a synth and a locked door with some loot.  After that, go left to continue the mission.
 * 8) A little further along, you'll hit an intersection; left leads to the mission marker, right to the "databanks," and straight to the front door where you would have arrived otherwise.  The databanks room has some background info and locked doors with a terminal that yield minor loot.
 * 9) Once you enter the last room before the marker, Deacon will open the vault and inspect a dead body. After the inspection, he'll offer you the "hand cannon" the dead man used and won't take no for an answer. Grab the prototype and head towards the elevator. Before you leave, to the right of the small set of stairs leading to the elevator is a locked door with an advanced lock where you can find another fusion core.
 * 10) Once out of the elevator, you get to kill all the synths you would have killed had you gone in through the front door.  Once they're dead, Deacon will go his own way and you can go back to the church to meet him.
 * 11) Once back to the church, you find Deacon lying to Desdemona about your exploits. You have the option to tell the truth or pass an easy persuasion check to go along with the lie.  Once you make your decision to accept or refuse the invitation to join, he mission is complete.

Option 2: Frontal assault
If you choose this option, you will fight through all of the synths and the machine gun turret which are guarding the Slocum's Joe front entrance. You will also need to circumvent or disarm all of the mines littering the front of the shop. Once inside, however, Deacon will give you the location of the hidden elevator only to realize it has been powered down, forcing you to use the escape tunnel entrance despite your successful assault.

Bugs

 * Deacon might stall in the hallway outside the room containing the locked vault and the Inaccessible terminal. Save and reload may clear this. Attacking and downing Deacon prior to the reload can also help.
 * When you are approaching The Old North Church to meet Deacon after getting Carrington's prototype, Deacon may suddenly move to the middle of the map making it impossible to meet with him. Loading a save game from the 'Get Carrington's prototype' step may solve this.
 * If the player passes the room with the locked vault and gets all the way to the elevator, Deacon will say "End of the Line!" and tell the Sole Survivor to turn on the elevator power. If you then go back to the locked vault, Deacon will stand in front of the terminal but he never uses it. Talking to him does not make him progress, either. He is the only one that can unlock the vault. Reloading a save from before passing this room fixes this. It is advised to open the vault before continuing down the hallway to the elevator.