The town of Megaton is one of the central points of Capital Wasteland and a vital stopover point for caravans crossing the region. Its name was not chosen at random: It comes from the unexploded nuclear bomb sitting in the center of the town. Although it has not exploded for two centuries, it's still a concern for the local sheriff, Lucas Simms... And the focus of a newcomer to town, one Mister Burke.
Disarming the bomb
The quest can be obtained while talking to Lucas Simms when the player enters Megaton for the first time or at any time afterwards. If the player offers to disarm the bomb, Simms will offer 100 caps as a reward. Passing a Speech check allows the player to haggle and raise the fee to 500 caps.
The player can head on over to the bomb and disarm it straight away. The player needs at least 25 Explosives to successfully render the weapon inert. In return, Simms will pay the player (if they did not mention a cash reward they receive 200 karma instead) and hand over keys to a vacant house in Megaton.
Mister Burke, the shadowy contractor interested in removing Megaton from the map, will disappear from the town. Talon Company will start appearing from time to time, ambushing the player in retaliation for interfering with Burke's job. James will compliment the player on their choice when encountered.
Detonating the bomb
The player can always take the opposite side. Doing so requires the player to talk to Mister Burke, who will explain that he is recruiting for the task of blowing the town up. If the player agrees to the job, the totally inconspicuous villain will provide them with a custom-made detonator, the fusion pulse charge, and direct the player to install it on the bomb and later meet him at Tenpenny Tower.
The requirements for installing the detonator are the same as for disarming the bomb, Explosives 25. The player then has to travel to Tenpenny Tower.
It's possible to turn Burke in to Lucas Simms. With the fusion pulse charge in hand, Simms will believe the player on the spot and confront Burke at the Saloon (note that telling on Burke and withdrawing the accusation will make it impossible to turn him in afterwards, Simms doesn't like people who flip-flop). Simms will immediately walk over to the Saloon and confront the villain. Burke will play along and agree to go to jail. For whatever reason, Simms agrees to lead the way. As expected, Burke will immediately draw a silenced 10mm pistol and shoot the sheriff in the back, killing him on the spot.
The player can save Simms' life by drawing first and gunning Burke down before he shoots the sheriff. As an impromptu deputy, the player is commended for saving Lucas' life. Burke can be killed at any time, actually, as long as Simms is heading over to confront him. If the player lets the sheriff die, Burke will give them a warning and then walk away to disappear. Harden Simms, Lucas' son, will then give the player the reward for disarming the bomb.
If the player character is female and has the Black Widow perk, they can instead seduce Mister Burke. Doing so allows the player to double the reward for blowing up Megaton (from 500 to 1000 caps) or convince him to abandon the job and spare Megaton. In this case, Burke will also send love letters, deposited at Moriarty's Saloon.
Once the bomb is rigged, the player has to reach Tenpenny Tower to the southwest. They will be let into the tower by the guards. At this point, all they have to do is meet with Burke and Allistair Tenpenny, his demented employer, on the upper terrace in the penthouse. Burke will let the player do the honors: Turning the knob in the briefcase will activate the charge and detonate the bomb, destroying Megaton. Everyone inside the town is killed instantly, any items left behind are lost, including Strength Bobblehead in Lucas Simms' house (without the use of console commands to access the town worldspace or cells), and the player instantly receives -1000 karma and keys to the Tenpenny Tower suite.
Moira Brown will survive and can be found outside the ruined town, suffering from massive radiation poisoning and burns, in the process of becoming a ghoul. After talking to her, she will relocate to the Underworld and offer the Wasteland Survival Guide quest as normal.
If the player completed the Tenpenny Tower quest for Roy Phillips and the inhabitants of the tower were slaughtered by the ghouls, Burke will still appear in the penthouse. He will successfully intimidate Roy Phillips, convincing him to let him finish the job and blow up Megaton. Afterwards, Phillips and Burke start a new partnership, impressed with each other's tenacity and absolute lack of a moral backbone.
Detonating the bomb will also insert an additional video into the ending reel, showing its destruction, and enable random encounters with Megaton refugees, who will attack the player. James will also complain about the player detonating the bomb, but it will have no lasting repercussions. Deputy Weld's head will also appear outside the ruined city, continuing to claim that the bomb is perfectly safe. Caravans will still stop at the ruined town's location, however.
Behind the scenes
The quest has been altered in the Japanese release of Fallout 3. Mister Burke is absent and it's impossible to detonate the bomb. Similarly, the Fat Man nuclear catapult has been renamed. In both cases, the changes were introduced to avoid mocking the victims of the atomic bombings at Hiroshima and Nagasaki in 1945.