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
Investigate the nearby town of Megaton for information about Dad.

In Megaton everyone will point you to Moriarty, who seems to know you and if you ask him enough he will say you were born outside the vault, and then taken in there and brain washed, he will tell you the whereabouts of your father if you give him 100 caps.

You can also use Speech to convince Moriarty that your father told you about him. If you have high enough Speech, you can get the information from him travel to GNR for free. Most NPCs will give you information freely upon persuasion, so ensure you up your Speech skill before the rest of the game.

If you lack the necessary caps, he will offer a discount if you agree to kill Silver and bring back the caps she stole, though you do not actually have to kill her. Also you might try to convince Gob into telling you those information, but it is implied that he will suffer Moriarty´s fury if he does. You can also hack his computer, or use lady killer on Nova, one of his employees, to gain the password. Make sure you speak to each named person in his saloon to obtain side-quests (Gob gives you the map marker for Underworld and discounts on the over-priced drinks, Lucy West will begin the Blood Ties quest). 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 up before continuing this quest.

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 to begin the long (but much safer) trek through the metro tunnels, expect to fight a ton of Raiders and Feral Ghouls.

Note: At the beginning of the first Metro Station, you will see the first sight of Ghouls confined behind a chain link fence. Do not open the fence, instead, turn around and enter the control room behind you. Open the metal boxes on the ground to get a Laser Pistol with Ammunition and a note. Reading the note will tell you the Laser Pistol can heat up gas to explosion point. Exit the room, arm the pistol and shoot the gas pipes near the ghouls. Voila! The pipes will explode, turning the ghouls into ground meat. This tactic will only work with pipes with gas obviously emitting from them which are rare.

Galaxy News Radio
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 to 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.

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 and the GNR building will be inaccessible. If you make it to the building (which is now permanently locked), you'll still encounter all the Super Mutants (including the Behemoth) with no Brotherhood of Steel soldiers in sight.