Gaining the knowledge necessary to both infiltrate the Mechanist's lair, and deal with them personally, the Sole Survivor and party travel to the RobCo sales and service center, which turned out to be a front for its inner, nefarious purposes.
Once inside, the party, utilizing the M-SAT, which much be attached to a robot in the party, will continually need to activate several devices throughout the facility, all of which will reveal more of the path that leads to the Mechanist.
Upon dealing with the robotic guards, the party will eventually reach the control room, where the Mechanist and their sidekick eyebot, Sparks, will spring an ambush, and send wave after wave of robots against them. There will be a brief moment to speak with the Mechanist, either normally, or by speaking as the Silver Shroud, should the Sole Survivor be wearing the costume, yet the Mechanist will always send the robotic waves against them.
As the waves are defeated, one after another, the power will begin to fail, forcing the Mechanist to eventually confront the party personally, in which the Sole Survivor will have a chance to end this confrontation, either by force, or through a silver tongue.
Should the Sole Survivor not portray themselves as the Silver Shroud, they will need to pass a Speech challenge in order to end the confrontation peacefully. Otherwise, the Silver Shroud dialogue will bypass the challenge, and the hostilities will end, with both the Mechanist and Sparks becoming permanent allies.
The Mechanist will take off the Mechanist helmet, revealing herself as a woman named Isabel Cruz. She will award the Sole Survivor the password to her mainframe, wishing it be in their hands.
Speaking to her again will award her armor and helmet, as she will give up the mantel of the Mechanist, and will also provide the radiant side quest, Rogue Robot, which will send the party against robots out in the Commonwealth, that are still attacking innocents.
Enter the Mechanist's mainframe and take control of the facility by cancelling the security alert with the master control terminal. Afterward, speak to Ada to finally give her closure on her friend's untimely deaths.
I discovered the Mechanist's lair has a hidden entrance in the old RobCo Sales and Service building. I should speak to Ada about my next move.
Install the M-SAT on a robot
I need to use the robot workbench to install the M-SAT into a robot of my choice. Then I will be able to gain access to the Mechanist's lair.
Access the Mechanist's Lair
I installed an M-SAT on a robot. I will need to keep the robot with me as I venture through the Mechanist's lair to be able to access the doors.
Stop the Mechanist
Now that I've gained access to the hidden facility, I need to find a way to the Mechanist to put an end to the robots terrorizing the Commonwealth. Several doors will require a robot with an M-SAT installed, so I'll need t be sure to keep one by my side.
Take Control of the Facility
Now that I have the passcode, I should find the terminal that will allow me to take control of this facility and stop the production of these robots.
Speak to Ada
Now that the Mechanist has been stopped, I should let Ada know that it's over.
While there is unique dialogue between the Mechanist should the Sole Survivor portray themselves as the Silver Shroud, there is no unique dialogue for donning the Grognak costume.
Upon ending the confrontation with the Mechanist, all robot mods will become unlocked at the robot workbench.
The quest may fail to recognize, again, that the player installed an M-SAT on a robot. On the PC, this can be worked around with the following command: