Following in His Footsteps

 is a Fallout 3 quest. It is also an Achievement on the Xbox 360 and PC; and a Bronze Trophy on the PlayStation 3.

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

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

In Megaton, everyone will point you to the saloon owner, Moriarty who will offer 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 (male character) to seduce Nova into giving you the password, or simply kill him and 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. The round dots in your Pip-Boy 3000 world map indicate intermediate points that are recommended, specifically, Metro stations, but you don't have to follow them, per se - just get to the goal, one way or the other. From there you will eventually end up at Galaxy News Radio, where you can follow a group of Brotherhood of Steel Soldiers (Lyons' Pride), 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 heavily damage the Behemoth (make sure you aren't standing too close as this weapon has an extremely large blast radius). Regardless, the marker still points to the dead soldier with the Fatman, so loot him for the optional points.

Depending on how fast you take the Behemoth down and who dies in the process, your conversation with the remaining soldiers goes differently. Use the intercom to the right of the door to get inside the GNR Building. 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.

The Search Continues
Killing Three Dog without getting him to tell you to go to Rivet City ends the GNR Quest and starts a new quest called The Search Continues. The objective is still to find Dad, your father can still be found at Vault 112 and you can still talk to Dr. Li.You do not get an achievement because it might be considered an "unmarked" quest, even though you can put it as an active quest on the Pip-Boy 3000

Skipping this quest
Note that this quest can be fast-tracked by skipping several steps:
 * visit Three Dog without speaking to Moriarty
 * retrieve the Project Purity Journals from the Jefferson Memorial
 * go directly to Doctor Li in Rivet City
 * travel 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.

Bugs

 * There is an occasional glitch where the Super Mutant Behemoth will not be triggered to appear. GNR will not open its doors, and the BoS soldiers will reach the fountain and then wander around the plaza aimlessly. If you speak to Sentinel Lyons, she will repeat her dialogue "You can tag along with us as far as GNR." A similar glitch occurs when, even after defeating the Behemoth, the doors to GNR remain locked, even though the BoS soldiers enter it. (confirmed Xbox 360, PS3)
 * It is possible that, after entering GNR and leaving right away, the generic BoS paladins will become hostile and attack you, if you kill any of them the others (Lyons, Vargas, etc.) will also attack and you will receive bad karma. (Xbox 360 confirmed)
 * Sometimes, the dead BoS Soldier does not spawn with the Fat Man.
 * If you decide to skip this quest by talking to Dr. Li or going to Vault 112 and come back later, Sentinel Lyons and her men will not appear when you exit the station, meaning you have to take out all the super mutants leading to the GNR building plaza. Also If you're not fast enough, the Behemoth will spawn before you get there. Note the Fat Man will not appear near the fountain or maybe not at all. So you are forced to fight the Behemoth without a Fat Man. (confirmed all platforms)
 * Sometimes, Sarah's squad will simply stop right before the plaza in the school building. The super mutants outside will not attack unless you attack them and the BOS soldiers will keep shooting the corpses after they kill the super mutants.