Mass Fusion

Warning: Doing this quest will turn the BoS into enemies.

Find Allie Filmore and talk to her to start the quest. If you're allied with the Brotherhood, you'll have the option to inform them about this move as well. Opting to notify the Brotherhood will start the Brotherhood questline directed towards the same location, Spoils of War. Once you board the vertibird, this quest will fail and you'll become enemies with The Institute. Take note that all other unfinished quests with them will automatically fail as well.

When ready, head to the relay from The Institute to reach the Mass Fusion Building. Before using the relay, you'll get the prompt that you'll become a permanent enemy of the Brotherhood. All pending Brotherhood quests will fail automatically.

You'll be transported in the Mass Fusion Executive Suite. There are already Brotherhood members here so take them out. You can't use the central elevator without the card so go upstairs and find the Mass Fusion Executive Lab Password and Executive ID on the desk.

Access the lab terminal nearby then login to the terminal. Read the very first entry to learn the location of the Agitator. Now use the ID card on the elevator and ride it to reach the Mass Fusion Building's interior. (For the loot locations, refer to the Mass Fusion Building's location page)

As the elevator is going down, you have to fight off several BoS members that will appear. When you're near the Glass door, the BoS members will blow up the conduit, powering off the elevator. You can either use the circuit breaker in the second floor or use the Development Manager's Terminal right below it. Once the Power is restored, you can now use the elevator again.

Kill the BoS forces here then head to the elevator to the NE and ride it down to reach the building's reactor room.

Reactor Room

• Prototype lab terminal to the SE can activate the protectron inside the room.
• Advanced Attendant's terminal can manipulate the security door, assaultron unit, and two laser turrets. You don't need to do anything anymore since the turrets and assaultron are all disabled, and the security door is already opened as well.
• There's a Hazmat Suit in the locker room to the SE
• Red steamer trunk in the middle west balcony, near the reactor window
• Small under the stairs to the middle-south has a Hazmat suit, novice Analyst's terminal, protectron pod, and Master Safe. The protectron and safe can be activated and opened using the terminal.
• Facilities Room to the north has two sentry bots, one is inactive and one will be activated once you grab the Berylium Agitator.

Talk to Dr. Filmore and tell her that you don't have any radiation protection to receive two Rad-Xs. When ready, equip the Hazmat Suit and use Rad-X. Go to the decontamination room to the SW and push the red button. Head inside the reactor, get to the controls and unlock it. Grab the Berylium Agitator then leave the reactor chamber. Proceed to the decontamination chamber then eliminate the sentry bot, assaultrons, and sentry bots. Once done, head to the elevator and leave the reactor room.

On your way out, the building will be breached by more BoS forces. Take them out then head back to The Institute and report to Dr. Filmore to complete the quest.