Mass Fusion Walkthrough | Fallout 4 (FO4)｜Game8 (2024)

Mass Fusion is an Institute Faction Quest in Fallout 4 (FO4). Read on for a full Mass Fusion walkthrough and learn Mass Fusion location and rewards.

Mass Fusion Quest Summary

Mass Fusion Walkthrough

Mass Fusion Objectives

1. Talk to Allie Filmore
2. Head to the Relay
3. Get the Mass Fusion ID to Ride the Elevator
4. Restore the Power
5. Take the Elevator to the Basem*nt
6. Locate the Beryllium Agitator
7. Unlock the Reactor
8. Take the Beryllium Agitator
9. Defeat the Hostile Securities
10. Exit the Mass Fusion

Talk to Allie Filmore

Speak to Allie Filmore to start the quest. As she tells you more about the assignment, you can invite her to come with you or ask her to stay behind. It's recommended to ask her to come with you, as you'll face a lot of Brotherhood of Steel hostilities along the way, and having extra manpower will prove valuable.

Head to the Relay

To reach the relay, board the main elevator in the main square and head up to the next floor. Exit the elevator and continue moving forward to reach the relay.

Using the Relay Will Make the Brotherhood of Steel Hostile

Keep in mind that proceeding further will automatically make you enemies with the Brotherhood. Only proceed once you've completed any active quests that you want to finish before Spoils of War.

Get the Mass Fusion ID to Ride the Elevator

Entering the relay will teleport you directly to the Mass Fusion building, where you will be immediately thrown into combat against the Brotherhood. Clear them out and take the Mass Fusion ID Keycard from the desk on the second floor, directly facing the elevator.

Restore the Power

Use the Mass Fusion ID to access the elevator. Head down and defeat all the Brotherhood forces attacking you as you descend. Near the middle of the tower, the Brotherhood will detonate a grenade, cutting off the power. You can restore it by accessing the fusebox on the left.

Take the Elevator to the Basem*nt

After restoring the power, board the elevator again to descend to the main floor. Once you reach the bottom, defeat any Brotherhood members you encounter before heading to the room on the left. Ride it to reach the Reactor Chamber.

Locate the Beryllium Agitator

After taking the elevator, take the stairs on the right and follow the path ahead. At the end of this path, you'll find the reactor chamber where the Beryllium Agitator rests.

Unlock the Reactor

Head to the room on the right and press the button to start the decontamination process. Immediately after the process, the door will open, and you'll enter a room with dangerously high radiation. Move quickly, as the radiation will cause significant damage that could kill you quick.

Bring Rad-X and RadAway

Make sure to bring plenty of Rad-X or RadAway with you to gain radiation resistance and heal radiation damage afterward. This helps you prevent from taking too much radiation, which in this room, could reach levels as high as 50 or more.

Take one Rad-X as soon as the door opens, and take a RadAway once you start taking too much damage!

Take the Beryllium Agitator

Upon reaching the top, press the Interlock Release and activate the Beryllium Agitator to acquire it. Head over to the entrance and start another decontamination process to exit the chamber.

Defeat the Hostile Securities

As you exit the chamber, you can rush back to the middle of the room to access the terminal located there. You can use it to minimize the pressure of combat by deactivating the Assaultrons. However, note that this terminal requires hacking to access the command, so make sure to add a few points to your Hacker perks before proceeding.

With the Assaultrons deactivated, you'll have more time to focus on defeating the Sentry Bots. These security bots are quite difficult to take down, but they can take significant damage from explosives like bottlecap mines. Additionally, having a companion by your side is beneficial, as they can distract the Sentry Bots, allowing you to attack without being targeted.

Exit the Mass Fusion

After defeating all enemies, return outside and meet Allie once more in the Institute to complete the quest.

You'll receive an optional objective to aid the Synths in eliminating any remaining Brotherhood forces as you exit, but this can be skipped as it does not affect the main storyline.

Mass Fusion Location

Where to Start Mass Fusion

Fallout 4 Related Guides

All Factions List

List of All Factions

Full Institute Questline