Destroy the Mutant leader Destroy the Mutant leader is a main quest in " Fallout " . The Vault Dweller has trekked across the Wasteland and brought the water chip back to Vault 13 , but the mutant armies still pose a dangerous threat to the safety of the vault populace . It is up to the Vault Dweller to stop their mad leader , the Master , and destroy whatever is creating them . Detailed walkthrough . The seemingly peaceful Children of the Cathedral have , up until this point , been a helpful ( if irritable ) organization , with their free hospitals in Junktown , Necropolis and the Hub . Now , the Vault Dweller needs to enter the Cathedral ' s walls to discover and defeat the evil within . The Cathedral is located two squares south of the Boneyard , and with Katja being the only person able to mark it on the Vault Dweller ' s map , one may need to search to find it . Once there , go through a staircase in the back of the main room . However , the door leading to that room is locked . To get there , a red COC badge must be obtained . Most of the Children in the main room , like Lasher , will carry one . Once the stairwell is reached , follow it down . However , another locked door blocks the path . Head up the stairs nearby and locate Morpheus on the third floor . The nightkin along the way up will be hostile to the Vault Dweller , unless they are wearing robes , are unarmed and alone . Morpheus ' death awards 1000 XP , and the black COC badge . Alternatively , he can be convinced to take the Vault Dweller directly to the Master ( see Speech solution ) . At the bottom of the hidden staircase , there is what appears to be a dead - end library . Searching the wall on the east side will reveal some intricate grooves . Lockpick or search the nearby bookcases for traps to reveal a lever and open a hidden passage . If it is after 8 P . M . , there will be a centaur and two floater s out in the caves , along with two armed super mutants regardless of the time . Enter the LA Vault . The first level is home to several more hostile super mutants the Vault Dweller will have to defeat to reach the elevator to get to the third floor . Once there , the player character is attacked by several Mister Handies , floating eye bot s and more super mutants . These must be defeated before heading down the corridor to where the overseer ' s chair would be . As the Vault Dweller walks down the corridor , they will get progressively worse messages in the message box , as well as taking Eye Damage , losing 2 points of Perception and Intelligence each by the time the far side is reached . This can be evaded by taking the Mental Block perk or taking a psychic nullifier from one of the psyker s on the 2nd level . At the very end lies the Master . Combat solution . The Master is a very powerful foe , with twin ( although dealing damage as one ) Gatling laser s , support from two floating eyes and a contingent of super mutants , but by now the player character should be a force to be reckoned with . Turn him into gooey paste for 10 , 000 combat XP , which is likely to level up the Vault Dweller . Once the Master is gone , the entire Cathedral goes into a self - destruct sequence . If the Vault Dweller is having some trouble killing the Master , and particularly if one ' s team has died by this point , forgo the dialogue and use one of the two pillars for cover to shoot out the eyes and mutant in - between shots at the Master . Once he explodes , use all the firepower left to finish off anything else and run like hell ( remember that timer ) . If the Vault Dweller does not make it out in time , they will die . As when the Vault Dweller blew up Mariposa Military Base , make sure to leave the map ; simply being outside the building won ' t count as having escaped . Speech solution . If the Vault Dweller does not want to kill the Master in combat , he can also be talked out of his plans for the Unity . The Vault Dweller can either convince him with the use of a very high Speech skill , or a slightly lower Speech skill and Vree ' s autopsy report . The Vault Dweller must have an Intelligence skill above six to obtain the tape from Vree ; once they read the holodisk , they can show the Master that all mutants are sterile . He will be unable to cope with the things he did in the name of the Unity , which he now knows to all be in vain . He will then tell them to leave ' while you still have hope ' and to find safe ground . He will commit suicide by detonating a nuke beneath the Cathedral . The player character must again have a high Speech skill to use Vree ' s tape as proof for the Master that the mutants will fail . However , use of certain perks negates the Speech alternative , and makes this ending unavailable ; even with maximum Speech level and Vree ' s tape . Nuke solution . If the Vault Dweller has either the Lieutenant ' s key from Mariposa Military Base or a very high Science level , that same nuke may also be used by the Vault Dweller . Get to the third level , but take a left once the intersection is reached . There will be a few more super mutants and an elevator behind them . Enter that elevator . Two mutants guard the nuke ; once they ' re taken care of , use the key to set the nuke for a four minute countdown . Be careful , if the Vault Dweller is still on the Cathedral map when it goes up , they go with it .