- Speak to Proctor Ingram
- Fly to Mass Fusion or Inform the Institute
- Jump to Mass Fusion Building's roof
- Locate the Beryllium Agitator
- Retrieve the executive key card
- Proceed to the Reactor Level
- (Optional) Restore power to the elevator
- Enter the reactor chamber
- Unlock the reactor
- Take the Beryllium Agitator
- Eliminate Reactor Level security
- Exit Mass Fusion Building
- (Optional) Assist Brotherhood forces in the lobby
- Return to Boston Airport
- Speak to Proctor Ingram
Speak to Proctor Ingram and agree to help her find a Beryllium Agitator from the Mass Fusion Building ruins. You can opt to have her come with you if you'd like. You are now faced with an important choice:
- You can fly to Mass Fusion Building via vertibird and drop down. This causes several of The Institute Quests to fail and this also triggers the Institute quest Banished from the Institute.
- You can leave and let the Institute know of the plans, switching your alliance. This triggers the Institute quest Mass Fusion
If you stay allied with the Brotherhood of Steel, you drop to the roof of Mass Fusion Building. Eliminate all the enemies here and go to the second level. In a desk on the balcony, retrieve the Mass Fusion Executive Lab Password and the Mass Fusion Executive ID. Accesss the research lab terminal with the password, and after reading the memos, head to the basement to obtain the agitator. If you hack the manager's terminal, you can power up the elevator and head down, or you must go to the circuit breaker.
Use the ID at the elevator and take it down as far as it goes. When you have cleared the area of enemies you either of the following:
- (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 to get to the lobby. Clear the enemies in the lobby here.
Once in the lobby, locate the service elevator and use the ID card to gain access. Step into the decontamination area, decontaminate and go into the reactor chamber. Activate the interlock release as well as the agitator receptacle. Taking the Beryllium Agitator will trigger the auto defenses. Go to the outer room, get past the Sentry Bot and Protectron and then use your ID card on the main door and dispatch the difficult Assaultron. Go up the stairs, past another Protectron and laser turret.
Exit to the lobby and assist your Brotherhood allies in dispatching the remaining enemies and then report to Proctor Ingram at Boston Airport.