Mass Fusion

The Institute Quest
Mass Fusion Building
Allie Filmore
Previous Quest
Mankind Redefined
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Mass Fusion is a Quest in Fallout 4. For the location see Mass Fusion Building.

Mass Fusion Information


  1. Speak with Allie Filmore
  2. A. Relay to Mass Fusion Building or B. Inform the Brotherhood
  3. Locate the Beryllium Agitator
  4. Retrieve the Executive Keycard
  5. Proceed to the reactor level
  6. (Optional) Restore power to the elevator
  7. Retrieve the Beryllium Agitator
  8. Unlock the reactor
  9. Take the Beryllium Agitator
  10. Eliminate reactor level security
  11. Exit Mass Fusion
  12. (Optional) Assist Institute forces in the lobby
  13. Speak with Allie Filmore




Rad Resist.png After speaking with Allie Filmore she asks you to find a Beryllium Agitator from Mass Fusion Building. She will offer to accompany you and it is your choice whether she does or not. You are then faced with a crucial choice:
  1. Relay to Mass Fusion Building to continue your loyalty with the goals of the Institute. Choosing this continues this quest, causes several of Brotherhood of Steel quests to fail and the Brotherhood quest Steel Shutdown begins. The game will prompt you with a warning as you are about to use the relay. If you relay, you are now an enemy of the Bortherhood.
  2. Leave the Institute and go to the Brotherhood of Steel with your information. This begins the Brotherhood quest Spoils of War.

Rad Resist.png Prepare yourself for a heavy firefight with firepower, ammo and healing. In particular, laser based weapons are recommended for this quest due to the amount of armoured enemies and robotic enemies you will encounter. Presuming you stay allied with the Institute, you will relay to the roof of Mass Fusion Building. Defeat all the enemies in the area and go down a floor to the executive suites. In a balcony desk before the room with a lab terminal you will find:
Access the terminal then with the password and read the memos to discern the location of the item, which you discover is in the basement.

Rad Resist.png Use the ID at the elevator and take it down as far as it goes. As the elevator descends, Brotherhood forces will attack you from balconies. Use your V.A.T.S. to take as many down as you want for easy XP. If you have Allie and a companion with you, you'll be able to make short work of them. Halfway down to the lobby the elevator will stop and you'll be in an atrium with a swam of Brotherhood forces. Clear the area out and you'll then have two options to progress:
  • (Optional) Access the circuit breaker above and flip the breaker to power the elevator. You may then take it down to the lobby.
  • Go to the room ahead, and find the Mass Fusion Labs Key. Use it to access the next room and drop down the hole in the floor, and descend level by level until you get to the ground floor lobby. Clear the enemies in the lobby here.

Rad Resist.png Once you've reached the lobby, clear out any remaining Brotherhood forces, then head to the left of the room to find a service elevator. Use the ID card to gain access. Follow the path down and you'll find yourself observing the reactor. Equip a Hazmat Suit or Power Armor and step into the decontamination area, decontaminate and go into the reactor chamber. Head up the stairs and activate the interlock release as well as the agitator receptacle. Taking the Beryllium Agitator will trigger the auto defenses.

Rad Resist.png Prepare yourself for a fight. Go to the outer room, and take on the Sentry Bot that will rush from one of the security doors. When you've defeated him, make sure to loot the remains to find several Fusion Cores. Next up will be a Protectron which you should be able to make light work of. Last up, however, will be two Assaultron enemies, one after each other. Be careful as they're VERY dangerous and very fast. Once they're all down, you'll be able to leave the reactor control room.

Rad Resist.png Return to the lobby and you'll have the option to simply escape, or help defeat the Brotherhood forces. Whichever you choose, once you're done head to the front door of the building and return to the Commonwealth. Warp to the Institute and see Allie Filmore to finish the quest.

Video Walkthrough

- JudasBlitzkrieg JudasBlitzkrieg - Mass Fusion Walkthrough

Notes & Notable Loot

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    • Anonymous

      I finished the game on railroad can fast travel off the roof all I can do is walk around can't leave and I need help plz

      • Anonymous

        Why can't I take a companion with me? I have been commanding one of the coursers and he goes with me to the relay area but doesn't reappear with me. Only Allie.

        • Anonymous

          If you have a high enough of a hacking level, you can hack into the reactor security room by hacking into the security terminal in the corner of the reactor room. There you can disable the security defenses and not have to deal with the Sentrybot once you leave the chamber!

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