Take it Back!

 is a Fallout 3 quest. It is also an Xbox 360 and PC achievement. Take It Back! is the final main quest, with the game ending immediately after its completion. In this quest, the player and the Lyon's Pride assault the Jefferson Memorial in hopes of activating Project Purity. A colossal, crude, yet brutally effective robot paves the way, annihilating numerous Vertibirds and Enclave soldiers, although it also destroys the force fields erected by the Enclave. However, the ill equipped Lyon's Brigade is massacred by a barrage of missiles and small arms fire, leaving the path strewn with the gruesome remnants of Enclave and Brotherhood of Steel soldiers alike. When the player and the remaining Lyon's Brigade members finally reach the Project Purity control room the player is presented with a difficult decision, to either activate Project Purity, and thus fill the Wastelands with life, allow Sentinel Lyons to activate Project purity, or inject a virus that will kill any irradiated beings who come into contact with water. However, the control room is victim to heavy amounts of radiation, enough to kill a human in mere seconds. If the player opts to resign themselves to this legendary fate, to purge the Wastelands of adverse water, they succumb to the radiation, for the betterment of humanity. Sentinel Lyons also assures the player that they will never be forgotten, and forever revered for their life-giving deed.


 * If the player has Fawkes as a companion, the Vault Dweller has the option to ask Fawkes to input the activation code for him/her when the time comes to decide who will enter the room. Even though Fawkes has a resistance to radiation, he will say "no", stating that this is the Vault Dweller's destiny.  It is not well explained, but it is possible that Fawkes' inherent radiation resistance would not be enough, or that he had other reasons for declining to assist the Vault Dweller in this manner.


 * The radiation in the control room overtakes the player when he or she finishes inputting the code, and apparently no amount of Rad Away, Rad-X, or Radiation Resistance is adequate to survive the ordeal.


 * There is no way to possibly continue playing after completing this quest. You can choose to go in there yourself, and enter the password 2-1-6 (Revelation 21:6), or you can make the Lyon's Elder's daughter do it. Either way, you finish the game. So make sure if you want to continue other side quests to save your game before you go into the Jefferson Memorial Rotunda. you can clear out the gift shop however, though the doors will lock behind you when you enter the rotunda.

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 * You can also simply wait for the Purifier to explode. If you do this then the ending movie is slightly different noting that you failed to fall in your father's footsteps and sacrifice yourself.

Ending Movies
The ending movie varies depending on how the player plays the game. The ending movie is made up of three parts: The beginning and end of the movie are constant and display the same movie regardless of how the game is played. The second part relates to the players karma and displays a different movie depending on the players karma level. The third part depends on how the final quest is completed, whether you send in Sarah Lyons or go in yourself and whether or not you inject the FEV virus.