Following in His Footsteps

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

This is the quest to find James, 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 caps. If you lack the necessary caps, he will offer a discount if you agree to kill Silver and bring back the caps she stole, thought 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 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 William'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.

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 launcher off the dead body of one of the soldiers (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, who will give you the Galaxy News Radio quest in exchange for information on where your father went. After completing this quest, he will direct you to speak to Dr. Madison Li in Rivet City, which will start the Scientific Pursuits quest.

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 supermutants (including the Behemoth) with no Brotherhood soldiers in sight.