Make your way back to The Prydwen (which you are likely at already) and find Proctor Ingram. She will mention that the next step to powering up Liberty Prime is to obtain a Beryllium Agitator, which they have located at a location called Mass Fusion. Ingram will tell you that she is coming with you as well. You can actually talk her out of it if you wish, but why not bring along another immortal character to draw fire for you? Tell her to come with you and head up to the main deck where a vertibird is waiting for you. Once you try to board it however, you’ll get the following warning:

WARNING: Boarding the vertibird to Mass Fusion will make you a permanent enemy of the Institute. Are you sure you wish to proceed?

Again, you should have made up your mind about your loyalties a while back, but you’ve been warned.

Mass Fusion Executive Suite¶

With the vertibird you will fly right to the top of the Mass Fusion building, discovering the “Mass Fusion Executive Suite”. You aren’t the first here though, the Institute is already here and as you know they are now your enemy. Thankfully, you have air power so go ahead and use the mini-gun and gun down all of the Synths you can (which is always a ton of fun). If your vertibird takes enough damage or if you kill all of the Synths you will be dropped off on the roof. Either way, clear all of the Synths out. Note that Proctor Ingram is considered essential and therefore can’t be killed.

Once you can, head in and up the stairs. You can head ALL the way up to a third level to find a door [Advanced] you can pick for a First Aid Box and goodies, as well as an outside area you can search for another First Aid Box. Head back down to the second level and across the way to see the Beryllium Agitator is not here, meaning you’ll have to go search the building. You can find the “Oslow’s Office Recording” holotape here. Give it a listen and then hack the terminal [Advanced]. Read the first email here to learn the Beryllium Agitator is in a reactor and you need the “Executive Keycard”. Lovely. Thankfully enough, just leave this room and check the desk nearby for the “Mass Fusion Executive Lab Password” and the “Mass Fusion Executive ID”. That was very easy! Use the keycard on the middle elevator here to proceed into the Mass Fusion building proper.

Mass Fusion¶

As you head down the elevator, you will be ambushed by Institute Synths. Use VATS to kill them on your way down and go into sneak mode to reduce your profile. Kill as many enemies as you can as they pop up, focusing on the doors to the left and right as you go down. When you do hit the floor, several more Synths will come out (valuing numbers more than power), so take them out as they show up. Once you are free to explore, head into the north room to find the “Mass Fusion Labs Key” on the table. There is also a manager’s terminal here that you can unlock with [Expert] hacking skills. This will allow you to re-route the power and completes the optional “Restore Power” objective. Also, be sure to head east from the glass floor, hanging a right and going forward until you find a ramp. Take that up and out to a destroyed balcony. Head right hugging the wall and you will wrap around to a room with a blue console you can wearch for a copy of Tesla Science .

If you can’t hack the terminal up above, you can head to the northeast corner to find an [Expert] locked door (or, with th ekey you picked up, a door you can open automatically) that leads downward. Do one of these things to allow us to continue heading downward.

From the lower floor, head up the left steps and into the left door to see an elevator with a key card reader. You can of course use this now, so enter in and head down. Once you get off, Ingram will point out the reactor, which you can see past the window. Before you head that way though, head through the south door to find the “Prototype Lab Terminal” with a lock [Novice]. Hack it and turn on a Protectron unit here, then go ahead and kill it. After that, go ahead and take the north door down to another office area. Here there is an “Attendant’s Terminal” [Advanced] you can hack to get several options.

Back out and save now, as you are about to let some enemies attack you. If you are handy with explosives, you can mine the two doors across from the terminal if you wish. Once you are ready, use the terminal to activate the Assaultron Units. This will make two of them come out of the doors so take them out. You are doing this so they don’t get to choose when to attack you, by the way. Next up is the turrets. Activate those as well and shoot down the one above the terminal and the one in the southern room. This locker room to the south mostly has junk, but the bathrooms beyond have a First Aid Kit you can loot.

Head back and into the reactor-viewing area. There are some balconies to the left and right and, at the end of the left one, a Steamer Trunk. Go ahead and loot it then note the mag-lock doors on each balcony. Yes, this facility is going to ambush you with these (lovely). Also note the area underneath the stairs, which has a hallway (which is odd) and doors with rooms off to the side. One of them has a locked “Analyst’s Terminal” [Novice] and a locked Safe [Master]. You can unlock the Safe with the terminal if you wish, but be sure to free the Protectron and kill it off like you did before.

OK, you are done with enemy prep work. All that is left is getting the Beryllium Agitator. You have to go into the reactor do that, and it is very radioactive, so if you don’t have your own Hazmat Suit, go to the locker room and get one from there. Put it on and then make your way to the decontamination room. Hit the button and enter the reactor. Make your way up to the reactor and hit the button, which will allow you to pick up the Beryllium Agitator.

Doing this sets off the security system. What you need to do right now is shoot the two Laser Terminals up on the ceiling to the west. Take them both out and you’ll be safe, then head back to the decontamination room. Hit the button and then put back on your regular armor. Inside the viewing area is one more Laser Terminal up on the ceiling and finally a Sentry Bot that comes in out of the north door. Chuck some explosives up there to soften him up and then take him on as he comes out. If it focuses on your AI teammates, lay into it like normal but you can also use the hallway under the stairs to take cover. Just beware of the explosion once it dies.

You now have to leave the building, so head east up the stairs and use your key card to open the door. Take the elevator back up and you’ll hear the Institute is still fighting. Once you get out, help the Brotherhood Soldiers clear out the Institute Synths in the lobby for the XP, then exit the building. Warp back to Boston Airport once you’ve left the building. Once you are at the airport, go ahead and talk to Proctor Ingram and after a small amount of dialogue (which varies a bit based on whether or not you let her come along to Mass Fusion) you will be done with this quest. Wait a moment and Ingram will start talking to you again (the break between talks is a bit weird, but oh well), which starts the quest “Ad Victoriam “.