In Fallout 4, a number of factions are vying for control of the Commonwealth. One of those factions is the mysterious Institute, initially introduced as a sort of the boogeyman of the game. But the player has the option of joining and helping them with their own questline. Mass Fusion is the third of those quests.
The quest in question involves the Sole Survivor going to the Mass Fusion building in downtown Boston to find an agitator which will start a new mass reactor in order to help with the Institute’s power needs. But like a lot in the game, there’s a bit more to it than you might think.
Beginning Of The Quest
Talk to Father in order to get the gist of the quest who will then direct you to Allie Filmore for more details. She will tell you that the Brotherhood of Steel is there and presumably looking for the agitator as well. It is important to note that doing this quest will make the Brotherhood permanently hostile towards you, so turn back now if you want to avoid that.
Allie will want to accompany you, but whether or not she comes with you is entirely up to you. It’s not essential to completing the quest. Regardless, head to the Relay Room and enter the relay to be teleported to the Mass Fusion Executive suite. A number of Brotherhood members will be there, so make sure you’re sufficiently equipped with good armor and/or power armor.
Inside The Building
Upon entering the first room, a keycard and password to the laboratory can be found located on a desk on the second floor of that room. Afterward, use the password to access the executive lab terminal to find out where exactly the agitator is located.
Once you are done searching the room, head to the elevator in the center of the room and use it. While riding it, Brotherhood members will assault you with a wide array of weaponry (including energy weapons) as you go down, until eventually cutting power to the elevator completely.
Restoring Power To The Elevator
When this happens, an optional objective will show up to restore power — there are two ways of doing this. The first is by flipping a circuit breaker found on the second level of where you were stopped. The second, which is not marked like the circuit breaker method, is by turning the power back on by using the development manager’s terminal on the first level.
The Reactor Level
After using the fixed elevator, you will arrive in the lobby and will then have to take another elevator to get to the reactor level. Once there, players will have to enter the level’s chamber to retrieve the agitator itself. But be warned, the room is infested with radiation.
Having power armor will protect you from this. But if you don’t have any then a hazmat suit will protect you as well. If you have neither of these things, one hazmat suit can be found in the nearby locker room on a shelf, and another is on a safe underneath the stairs leading to the reactor chamber.
If have a high enough hacking skill, a security terminal can be hacked that will open the doors to the facilities terminal, next to a downed sentry bot. Not doing this and removing the reactor will trigger an alarm and cause a number of automated defenses to start attacking you.
After retrieving the agitator, return to the lobby to see Institute synths fighting it out with the Brotherhood. It is not necessary to help the synths, but you can for some extra XP. Regardless, leave the area and talk to Allie one last time to complete the quest.
