Picking Up the Trail

 is a Fallout 3 quest. It is also a Xbox 360/PC achievement and a PlayStation 3 Trophy.

Gain entrance to Vault 87.

Scribe Rothchild
Scribe Rothchild can usually be found in the lab of the Citadel. If you are in a hurry you can just access the Vault-Tec Terminal (Vault 87 section) in the A Ring without consulting Rothchild. If you ask him, all he will tell you is the location of the Vault-Tec Terminal.

Once you've consulted the terminal, Rothchild will show you its location on the lab map panel. He also warns you about high levels of radiation around the vault's main entrance, which leads him to hint at the location of Lamplight Caverns.

Little Lamplight Caverns

 * See also: Little Lamplight, Rescue from Paradise

Mayor MacCready will stop you at the gates of Little Lamplight. You can convince the mayor to let you in with a Speech challenge or with the Child At Heart perk. Failing the challenge, the only way into Little Lamplight is to help rescue Sammy, Squirrel and Penny from Paradise Falls by doing the side-quest Rescue from Paradise (which is an Xbox 360, PC achievement, and Playstation 3 Trophy). An alternative is to just reload the save.

Once in Little Lamplight, there are three ways to get to Vault 87:
 * 1) Survive Murder Pass. You must speak with Mayor MacCready or Princess to get the gate to Murder Pass open.
 * 2) Learn from Mayor MacCready that there is a door that won't open. This is a back door to Vault 87. You must ask Joseph to restore power to the computer terminal before you can use it. The door and terminal (average difficulty) are located in the Great Chamber.
 * 3) Another option: Restore the power to the computer terminal, decode the lock but don`t go through the door yet otherwise you cannot get back should you want either through this door or back through murder pass but will end up prisoner at Raven Rock. Instead back track to Mayor MacCready and ask him to open the back door. Clear out and ransack murder pass, clear out and ransack Vault 87 but do not let Fawkes go to the G.E.C.K. otherwise you will immediately trigger the Raven Rock capture sequence since you cannot now escape the vault. Instead, take all loot from Vault 87 and trade it on the open market for the fun of trading. Then you are free to decide when to go back to Fawkes using either Murder pass or the rear computer password locked door to obtain the G.E.C.K. Don`t forget the Nuka-Cola Quantum in the vault.

Bugs

 * If Princess is located near Murder Pass when you convince MacCready to open the gate, there is a chance that she will become stuck in the closed gate, preventing MacCready from opening it. If this happens, the only way to continue is to take the alternate route through Joseph.
 * It's possible that this quest will be considered "completed" and move you onto the next quest before you get into Vault 87.
 * It is unknown the cause of this bug but when you first access the computer to learn of the G.E.C.K. you will be prompted to go see Rothschild but he is nowhere to be found and on the map he is away from the citadel so it impossible to see him.
 * In the PS3 Version(confirmed on Xbox 360 version also), if Scribe Rothchild is not located in the Citadel labs and is instead in the A Wing when approached about Vault 87's location he will say to follow him but will not immediately return to the labs. Instead he will leave through the courtyard entrance and will return to the Citadel's labs after about 2 in-game hours. From this point he will have no further dialogue after returning to the Vault-tec location map, and will engage with other NPC's but not the player.