You ready to Take your Brotherhood of Steel to the maximum level by eliminating all the foes such as The Institute and the Railroad. You need to be prepared for the worst fight as you will be disloyal to the other Factions. Let's check the Fall of the other faction in this Last Part of Brotherhood of Steel Essential Quest.
It's time to end the Railroad's journey by eliminating all the Leader of this faction. You need to take them one-by-one in the Old North Church and gain your position in Brotherhood.
Objective
Walkthrough
If you accept Lancer-Captain Kells mission to eliminate the Railroad Leader then your relationship with them will be over. It's better to complete the necessary quest with them to gain some unique collectible or Armor. If you decided to stick to the mission then go to Prydwen and speak with Lancer-Captain Kells.
Now head to the Old North Church where the Railroad's elite is waiting for us. Once you get inside the church, start eliminating all the enemies and continue moving inside the Church Crypt then in the catacombs. Here you need to activate the detonator to destroy the wall and get through it towards the Railroad base.
Once you enter the Base, start executing the Leaders: Doctor Carrington, Glory, Tinker Tom, Deacon and Desdemona one-by-one and make sure no one is alive. Now that the Railroad is down you need to locate the PAM and either you destroy it or reprogram her. Exit the Church and get back to Prydwen to inform Kells about the success. If you chose to reprogram the PAM then she will be moved to Prydwen. Thus ending the Mission with the Fall of Railroad's Elite.
Another tough Decision to make if you want to get along with the Institute or Stick to the Brotherhood of Steel till the end of the Story. This guide will provide you both the cases so let's check them out.
Objective
Walkthrough
After you have a word with Proctor Ingram where you agree to help him find Beryllium Agitator from the Mass Fusion Building. Here you have to decide:
Presuming that you stay aligned with the Brotherhood then take the Vertibird and land on the Roof of the Mass Fusion Building. Once you enter the Ruins start executing all the enemies inside then get to the second floor and grab the Mass Fusion Executive Lab Password and the Mass Fusion Executive ID to access the Lab terminal and the elevator to head down with this Password.
Now Head to the Basement and retrieve the agitator then try to hack the manager's terminal to power up the elevator or simply go to the circuit breaker to start it up. Again use the elevator with the ID then head down to clear the next bunch of enemies and now you have two options:
From the Lobby, clear the enemies and head straight towards the decontamination area where you will find the reactor chamber. After activating the interlock release and the agitator receptacle go ahead to take Beryllium Agitator. Get ready for some hardcore action where you need to pass the Sentry Bot and Protectron in the outer room and then Assaultron at the Main door.
As you reach upstairs another Protectron and Laser Turret are waiting for us. Finally make your exit from the lobby and then you can either assist you allies with the remaining enemies or directly fly to Boston Airport to report Proctor Ingram thus ending the Mission and finally gaining Brotherhood trust.
You get to use the Liberty Prime who will now be activated with the help of Beryllium Agitator. Let's get the Synth of the Track and show them who is the real boss.
Objective
Walkthrough
You have acquired the Beryllium Agitator from the Mass Fusion ruins, go to speak with Proctor Ingram and he will guide you with the powering up Liberty Prime. Go to Liberty Prime and insert Agitator behind Prime's head. Now that the Agitator is placed its time to power up the Liberty Prime by activating the power switch.
Liberty Prime is now ready for action, use it to Travel to C.I.T. ruins and take all the Synth down. Here you also need to take care of the Prime from taking critical damage. Thus Ending the Mission and You are ready to take the Final Ending of Fallout 4 with Brotherhood of Steel. Now is the Beginning of Act 3: The Nuclear Option Brotherhood of Steel.