MAIN QUEST 5: Following in his footsteps
Received from: automatically once you've left Vault 101 [Capitol Wasteland]
Solution: Your first assignment is to get to the city of Megaton which is located to the south-east of Vault 101. Travel in a straight line if you don't want any problems. Talk to sheriff Lucas Simms once you've arrived at Megaton. When you agree to participate in his side mission (The power of the atom), Simms will tell you that you should ask Colin Moriarty for the whereabouts of your father. You can find Colin in his saloon. The exact location is Megaton - Moriarty's Saloon. Talk to Colin once you've arrived at your destination (screen) and ask him about your father. Colin will tell you that James wasn't the first one who left Vault 101. You will find out that he was going to visit Galaxy News Radio station. If he doesn't want to tell you the answer, you can consider bribing him or you can do him a favor by resolving a small problem in Springvale. Check the second part of the guide for more info (look for the description of Small Ranch in Springvale). Alternatively you can find the location of James from Moriarty's computer, but this would require some science skill to hack into his system. You can find the terminal in one of the back rooms of the saloon.
Exit Megaton. As you've probably noticed, you will have to get to Galaxy News Radio building which is located in the D.C. ruins. It's not going to be easy, so I wouldn't recommend travelling there unless you're level 7-10 and with decent guns/armor at your disposal. There are a lot of centaurs and supermutants in the area (surface), as well as feral ghouls and mirelurks (underground tunnels, sewers). The easiest way to get to the radio station is to use some of the nearby tunnels. Travel to Farragut West Metro Station and enter the subway. You will encounter some molerats along the way. You can destroy all of them by yourself or you can find a security terminal in order to activate a protectron. If you decide to rely on the robot, make sure that you have a subway ticket in your inventory, because otherwise you'll end up being attacked.
Eventually you'll get to an area occupied by large numbers of feral ghouls. There's a security terminal in one of the side rooms. Using it doesn't require any skill and you can use it to open a safe with items of great value. There's a closed gate blocking your way. Use bobby pins to open it or go back to one of nearby offices in order to find a proper key. Either way, you will have to deal with all ghouls before moving on. I would recommend shooting at the generators, because the explosion should kill them or at least most of them. Eventually you should be able to reach an exit which leads to Tenleytown / Friendship Station. Use it. Sadly, you will come across a single supermutant here, so be careful while trying to kill it. Keep shooting at the ghouls as well. Get to the southern exit (screen). It leads to Chevy Chase - North.
Notice that you've left the subway tunnels to the north of the Galaxy News Radio building. You will soon encounter paladins from the Brotherood of Steel. DON'T attack them, because they're your potential allies at the moment. Instead, help them in defeating the first group of supermutants. Stay in the back, however try dealing the last shot to each supermutant and you'll gain much needed experience. Once it's safe, talk to Sarah Lyons (screen). You will find out that her squad is heading towards the radio station building, so it would be a good idea to join the paladins. The group will soon enter a large and partially destroyed building. There are a lot of supermutants here, but your new colleagues will deal with all monsters. Stay in the back and you'll be safe. I would recommend inspecting the body of knight Jennings. You can't wear his power armor just yet and I wouldn't recommend carrying it, because it's very heavy. Don't worry - you will receive proper training in power armor usage during one of the upcoming main quests. For the moment the only thing you should consider taking is his laser pistol.
It shouldn't take too long for you to reach Galaxy News Radio building. You must help paladins in defeating the final group of supermutants, including a very powerful supermutant master. Once it's done, wait for a behemoth to show up. Locate a body of a killed paladin quickly (screen) and take his weapon - a fatman. This gun fires mininukes at the target. Choose the fatman from your inventory and fire at least one nuke at the behemoth. If you're successful, the beast should lose at least half of its health. You can fire again at the behemoth or you can use other weapons to finish it off. Minigun is always a good idea, as well as a rocket launcher. Prevent the monster from getting too close, because you would have been killed with one successful blow. Check the body of the behemoth once it's dead and you'll gain access to a lot of random items. You may also scout the area for bodies of other fallen paladins. Most of them were carrying good weapons.
You may talk to Sarah Lyons again when it's safe and she'll thank you for all the help you've done in defeating the supermutants. Proceed towards a large building. Use the intercom and after a while you will be granted access to the radio station. You can explore the entire building if you want to and you can also talk to present brotherhood members. In order to fulfill your current challenge you must use the stairs to get to the first floor. Locate a single door which leads to RGN Studios. The person you'll have to talk to is Three Dog. You can convince him to tell you where James has gone (screen), but you must have a high speech value to succeed in this challenge. You can also agree to doing him a favor. You'll find out about the transmitter and how to repair it. Proceed to the description of the next main quest.