Mass Fusion (quest)

Mass Fusion is an Institute main quest in Fallout 4.

Quick walkthrough

 * 1) Speak with Allie Filmore.
 * 2) Relay to Mass Fusion building or 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.

Detailed walkthrough
The Institute is ready to initiate Phase Three of its long-term plans. Phase Three involves starting a new mass reactor that should resolve the Institute's ongoing power needs. To start the reactor, the Facilities division first needs to obtain a Beryllium Agitator, a device used to "jump-start" the reactor. Father tells you to speak with Allie Filmore for the details of that operation.

Dr. Filmore explains that the Mass Fusion building in downtown Boston is known to have an agitator on-site, but retrieving it has become problematic because The Brotherhood of Steel is at the location. Allie assumes that the Brotherhood is also looking for the agitator, and she wants to make sure the Institute gets to it first. She also insists on coming with you, promising not to get in the way but not totally trusting you with the delicate technology. If you prefer not to have her along, you can tell her flat-out that she isn't coming because she'd just be a liability. She will be insulted but will not accompany you.

When you're ready to continue, take the central lift up to the Relay room. Upon entering the relay, you should get a warning that relaying to the Mass Fusion building will make you a permanent enemy of The Brotherhood of Steel (and fail any BoS quests you have in progress). Continue and you'll be teleported to the roof of the Mass Fusion building.

When you arrive at the Mass Fusion building, there will be Brotherhood faction members present throughout the building. As with other factions, you must fight your way down through the building, obtaining an Executive Keycard and re-routing power to the elevator when it stops. When you reach the reactor itself, you'll need to enter the chamber and remove the Beryllium Agitator from the reactor. The room is heavy with rads, so make sure to wear a Hazmat suit or power armor.

Once you remove the agitator, alarms will sound and you'll have to deal with several waves of security robots. Once you leave the reactor area, you will find Brotherhood & Institute faction members fighting. You can either leave immediately or choose to help the synths clear the BoS soldiers.

Speak with Allie Filmore again to complete the operation, then Father to start the next quest, Pinned.

Behind the scenes
A beryllium initiator is used to generate neutron flux for starting nuclear fission reactions.

Bugs

 * The survivor can occasionally appear underneath of the rising elevator when taking it from the ground floor to the executive suite. You can use to get back onto the elevator.
 * There is an occasion when using elevator to proceed down to the underground sector where the beryllium agitator is, Allie Filmore will appear in the elevator in the exhausted state, even though she is at full health. This makes the situation become awkward as you have to proceed the quest alone from then on, to the last of the quest.

Mass Fusion