MAIN QUEST 10: Picking up the trail
Received from: Doctor Li [Citadel]
Solution: The first part of this mission is going to be very simple. All you have to do is to follow Doctor Li. Eventually you'll get to a gate which leads to Citadel - courtyard. Travel to that location. Once you're inside the Citadel, listen to a conversation between Doctor Li and Elder Lyons. Talk to Li and Lyons when you have the chance. Li will order you to find Scribe Rothchild in order to gain access to the archives. In order to find Rothchild you must travel to Citadel - lab. You can access this area from the courtyard or from the A ring. It shouldn't take too long for you to find Rothchild (screen). Inform your new ally that you must find a working G.E.C.K. Rothchild will say that you'll have to access a Vault-Tec computer in order to find out which vault has received the G.E.C.K. Proceed to Citadel - A ring.
You can find the Vault-Tec computer in the southern area of the A ring. Locate a working station and use it to gain access to the system. You'll have to start off by ordering the computer to display the list of all vaults built in the Capitol Wasteland. Choose Vault 87 and display the list of equipment for this vault. You should notice that G.E.C.K. among other things. You may go back to Scribe Rothchild, so this means you'll have to go to Citadel - lab again. Ask Rothchild to show you where Vault 87 is located. Approach a large map (screen) and notice several vault icons. The same locations will be added to your Pip-Boy. Talk to Rothchild again. He will warn you that it's not going to be easy to get to Vault 87. You must return to Capitol Wasteland and this means you'll have to exit the Citadel.
Rothchild has suggested that you should visit a town called Little Lamplight which is located to the south-east of Vault 87. Obviously you should follow his advice. If you haven't visited this area before, start the trip from Smith Casey's garage, because it's probably the closest marker on your map. Once you've arrived at Little Lamplight ignore the buildings located on the surface. Proceed to a small entrance near the rocks (screen). It leads to Little Lamplight - caverns. Try moving forward and after a short walk you are going to be stopped by Mayor MacCready. He's in charge of this town populated entirely by children. You must resolve this situation peacefully, however there are two ways for you to gain access to an underground town. If you have a high speech skill you can convince the mayor to allow you to get to Vault 87, because you're on a very important mission. Otherwise you will have to do him a little favor. MacCready will mention that a few kids have been kidnapped by the slavers. You must rescue them. Read the description for Rescue from paradise quest if you want to find out how to do this.
Once you've gained access to the Little Lamplight, you should talk to Mayor MacCready. Ask him how to reach Vault 87. MacCready will mention a locked door, as well as a very dangerous passageway, called Murder Pass.
Choosing the door:
If you decide to use the locked door it's going to be much easier to get to Vault 87.Travel to Little Lamplight - great chamber and find Joseph. Ask him to reactivate one of the security terminals. Find the door MacCready was talking about (screen) and you should be able to locate the terminal nearby. If your science skill is high enough, you will be allowed to hack into the system. This will allow you to gain access to the security system of the vault. Choose Open door function from the menu and travel to the Reactor room. You will find yourself standing inside Vault 87 and this quest will come to an end.
Choosing Murder Pass:
Travelling through the Murder Pass is more dangerous, but it's the only way if you can't hack the terminal. It would be a good idea to ask MacCready to show you the way to the entrance to Murder Pass. It's located in the northern section of the caves. Once you've arrived wait for him and the Princess to open a large gate for you. Proceed to a new door and confirm that you want to travel to Murder Pass. Get ready, because these caves are being occupied by a lot of supermutants. It's not going to be easy, especially since they like to travel in groups and you'll also be dealing with their more powerful versions. Avoid larger rooms and instead choose smaller passageways. Keep heading north until you've reached an entrance to the vault (screen). Open the door. Watch out for a pressure plate to your right, because it's a trap. Move to the north and find the entrance to the Reactor room.