Following in His Footsteps

 is a Fallout 3 quest. It is also an Xbox 360 and PC achievement.

This is the quest to find the Vault 101 Dweller's father, James, who mysteriously disappeared from Vault 101.

Megaton
Objective: Investigate the nearby town of Megaton for information about Dad.

In Megaton everyone will point you to Moriarty, by talking to he offers to tell you where your dad is if you give him 100 caps. If you do not have the caps Moriarty will charge you 300 the next time you talk to him. You can also use Speech to convince Moriarty that your father told you about him. If you choose certain dialogue options then he may offer a discount if you agree to kill Silver in Springvale and bring back the caps she stole, though you do not actually have to kill her.

If you choose the bad Karma way to interact with Moriarty, you can steal the password to his terminal out of a locker next to it, or use Lady Killer to seduce Nova into giving you the password, or simply loot the password off his dead body (make sure you speak to each named person in his saloon to obtain side-quests). However you obtain the information, it leads you to Galaxy News Radio. Getting to GNR is not a walk of the faint of heart however, so make sure you level and gear up before continuing this quest.

Galaxy News Radio
Head to Super Duper Mart and from there to Wilhelm's Wharf, where you will meet an old lady who has some food for sale. Somewhere along this route, you will meet Bryan Wilks (if you haven't already) who begins the Those! quest. Cross the river (swimming the radioactive river is not advised) over the intact bridge found not far away. You will run into Super Mutants and Raiders. Head for the first Metro Station you can find (for instance Friendship Heights or Farragut West Metro Station) to begin the long trek through the metro tunnels, expect to fight a ton of Raiders and Feral Ghouls. If you follow the tunnels correctly, you should exit in Chevy Chase.

From there you will eventually end up at Galaxy News Radio, where you can follow a group of Brotherhood of Steel Soldiers (Lyons' Pride Platoon), led by Sentinel Sarah Lyons in an assault on the Super Mutants, Super Mutant Brutes, and Super Mutant Masters attacking the GNR building. The boss character for this assault is a Behemoth (mutant). It is best advised to pick up the Fatman nuclear launcher off the dead body of the Brotherhood soldier in the central fountain (there is a map marker pointing to it) as this will cut the Behemoth's life in half with one hit (make sure you aren't standing too close as this is an AOE weapon). Depending on how fast you take the thing down and who dies in the process, your conversation with the remaining soldiers goes differently. Once inside, talk to Three Dog. You have two options at this point. If you have high enough Speech, you can persuade him that your father will aid his cause upon your rescue. Doing this will give you the Scientific Pursuits quest for free. However if you have insufficient Speech, he will give you the Galaxy News Radio quest in exchange for the quest.

If you used Speech successfully, make sure to talk to Three Dog again. He will offer to exchange the location of a large cache of military munitions in return for the Galaxy News Radio (quest). This allows you to explore the quest for greater returns.

After completing this quest, he will direct you to speak to Dr. Madison Li in Rivet City, which will start the Scientific Pursuits quest.

NOTE: Be careful with the Fatman, if you hit one of the BOS soldiers, they will turn hostile. NOTE 2: Remember to loot any dead BoS Soldier's Power Armor and Helmet. You can use them as repair material for later. You will also be able to sell the holotags to a brotherhood librarian later on, so keep those as well.

Skipping this quest
Note that this quest can be fast-tracked by skipping several steps - you can go to Three Dog without speaking to Moriarty, go directly to Doctor Li or even to Vault 112, where James is imprisoned.

If you end up finding Vault 112 before visiting Three Dog at GNR Plaza, this entire quest will be marked as completed. If you make it to the building, you'll still encounter all the Super Mutants (including the Behemoth) with no Brotherhood of Steel soldiers in sight. The door to GNR will be locked but if you use the intercom after the mutants have been all been killed, the Brotherhood of Steel soldiers stationed inside will let you in. You can then speak to Three-Dog and get the Achievement for Following in His Footsteps. Additionally, he'll offer you the Galaxy News Radio quest in exchange for the key and coordinates to Hamilton's Hideaway.