At the end of this quest you'll be given the choice of either obliterating the Enclave base or taking out the Citadel. Know that doing the latter will make all of the remaining Brotherhood of Steel members pretty cheesed off at you. Given that this is the case, and given that two of the three new side quests available with this DLC are provided by Scribe Bigsley at Project Purity, you may want to go and do those now if you're feeling particularly homicidal. Head to the "Side Quests" section of this guide for all necessary side quest information.

After talking to Paladin Tristan and finding out that you're on your own again, gear up and fast travel to Metro Center. A bunch of Super Mutants will greet you so take them all out and then follow your marker westward until you get to the another group of Super Mutants fighting it out with some Brotherhood of Steel paladins. Help out, or don't, then head past the paladins towards the manhole cover surrounded by cones. There's some gear near the manhole cover, so grab whatever you need, then head on down.

You can loot the room directly to your right for weapon parts, and use the workbench to build whatever you want. When done, leave the room and enter the opposite doorway. Keep following the hallways until you get to a door on your right that leads to the Presidential Sub Level. Once you enter the Sub Level, there will be a Sentry Bot patrolling around, so take it out and then loot the place for ammo.

Keep heading forward through the tracks (it's a linear path), taking out the turrets and Sentry Bots as needed until you come to a room with a large computer. That's MARGoT. Say hi, MARGoT. With a speech check or a high enough Science skill you can convince MARGoT that you're a friendly which will allow you to travel on unmolested by robots. If you can't be marked as friendly you'll now have robots and Ghouls to deal with, that is unless you have the Ghoul mask. You did remember to bring your Ghoul mask, right? *sigh* It’s like you don't even listen. Any way, MARGoT will tell you that she can't make the trains run on time until you find a fuse or clear out the security breach, the security breach being the ghouls that have overrun the train tunnels. Once you're done talking to her deal with the turrets and robots she sends your way if you couldn't convince her to let you pass and then head through the door to the Presidential Metro.

Once you enter the Presidential Metro proper you'll come across a fight between robots and Feral Ghouls, Feral Ghoul Reavers and Glowing Ones. If everyone thinks that you're friendly, well just stroll on through. If no one or only some of them think you're friendly, kill whoever is hostile. Keep on working through the tunnel until you get to a door on your left. Go through the door into an equipment room, pausing to go through the first aid kit as well as to pick up the laser rifle and Nuka Cola Quantum, and then head into the other tunnel.

Keep heading forward until you come to the Presidential Metro Sentinel Unit. Kill this big boy and loot his remains for the fuse. Ok, now look around and you should see a fuse box arcing with electricity. Don't do anything yet. Put your back to the fuse box and walk forward until you come to a locked door. A Sentry Bot will come out of this door and the one to its right, past the flag, once you mess with the fuse box, so if you have any pulse mines, lay one down in front of each mine, equip your best robot killing weapon and then grab the fuse. If you have any bottlecap mines, a pulse mine - bottlecap mine combo will probably take out each robot in one shot, or at least leave something easily mopped up. Before you get on the train, you can head up some stairs and find a holotape named "Sorry my darling". This holotape will allow you to complete the unnamed quest "Fatal Attraction". Once you're all done in here get on the metro and activate it. Ain't mass transit grand?

Now that you're in Adams Air Force Base, you'll have plenty of Enclave troops to deal with, so switch over to whatever kills them best. Go up the stairs and pick the locked door on the left so that you can sneak up on the nearby troops as well as hack a terminal to turn off the turrets. If you can't hack it, just go in guns blazin'. Once everyone is dead, go up the stairs and enter the Air Force Base proper.

Once in the base, head up the stairs and then to the left. Your destination is the crate next to the elevated trailer. Open it to get some ammo, your orders and a brand new Tesla Cannon. Take your new toy and follow your compass towards the marker, taking out turrets with the Tesla Cannon as needed. The Tesla Cannon is a one shot kill on Vertibirds so make use of this whenever the Enclave try and crash your party. You won't get experience for the kills though, so if you're looking to level up, you can always wait for the troops to arrive and then take them out one by one.

Make your way to the airstrip surrounded by hangars and enter the only open one. Take out all of the Enclave in here. Do not let the Deathclaws out as they can not be controlled by your device and they will kill you or at least try. If you want the easy experience, feel free to kill them from outside their cages. Leave the hangar through the other side and be wary of a roaming Sentry Bot. The Tesla Cannon should take care of it in short order. Once you pass under the walkway and into the next area you're going to have a lot of Enclave soldiers to deal with, so just find cover where you can and slug it out. When you get to the air control tower looking building, head up the stairs, taking out turrets as necessary until you can enter the tower.

There's a Sentry Bot here in the tower that you can take out or ignore and just head up the stairs. Hit up the first aid kit at the bottom of the stairs before heading upwards. Once you get to a door marked "Adams Air Force Base" head through it. Check the first aid kit on the ground for some aid and then access the terminal and choose the "Open Mobile Platform Loading Ramp" option. Do not hang around in this tower as a bunch of Vertibirds will appear shortly and make your life difficult. Once you're done with the terminal, leave and go all the way back down to ground level and more fighting. Keep an eye open for enemies on the roof on the base. If you have the Gauss Rifle, there's a good chance you can pick them off. Just be persistent and eventually they should fall. Once everyone is dead, follow your compass, but pause to raid the open trailer for goodies. When finished, go up the ramp and open the door to the Mobile Base Crawler.