Underground Undercover is a rather lengthy quest in Fallout 4, which will see the Sole Survivor work alongside the Railroad to organize a Synth rebellion within the Institute. It’s a main quest for the Railroad faction in Fallout 4, and will also unlock an achievement/trophy related to the quest itself. Yet, with so many steps, and an unclear endpoint, it might service players well to know a full guide to Underground Undercover.
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Be warned, the total completion of this quest will forever alienate two factions, and if players go through with Underground Undercover, they will need to act as a double agent by playing the Institute, thus forever making enemies with the Institute and the Brotherhood of Steel when all is said and done, which is a far worse fate than any deathclaw could be.
Talk To Desdemona & Tinker Tom
To receive the Underground Undercover quest, players must still be aligned with the Railroad, and have successfully infiltrated the Institute without hostilities through The Molecular Level quest. Returning to the Railroad HQ, players can talk to Desdemona, who wants to try and find the man responsible for freeing Synths from within the Institute.
Talk to Tinker Tom, who will task players with using an encrypted message holotape to try and discover the identity of their man on the inside, who they have codenamed as Patriot. Once the holotape is acquired, players need to head back to the Institute, which is made accessible only through fast travel on the Pip-Boy.
Access Any Terminal Within The Institute
Now inside, players simply need to find a terminal. Not to worry, as there are plenty of them around. The most obvious find is heading back to Father’s room, where players will be able to access his terminal. Once inside the terminal, players will want to select the Load Holotape button, and then search and select Encrypted Message Holotape.
Once this has been loaded into the terminal, copy Tom’s message to upload it, and back out of the tape to await a reply from Patriot, which will occur instantly. Head back into the holotape and select Read “UrgentReply001” to receive the next step, which is to meet Patriot himself.
Meet Liam Binet
Heading into the cafeteria between the Advanced Systems and Bioscience rooms, players will find a little janitor’s closet to the right of the stairs. Heading inside to the furthest room on the right, they will find Patriot waiting for them, who turns out to be an Institute scientist, Liam Binet, who is all too innocent and excited at the prospect of helping the Railroad free Synths. After talking to Liam, he will beckon players to follow him as he takes them to meet a Synth named Z1-14, who divulges a plan to free thirteen Synths all at once.
Head To The Railroad HQ & Speak With Desdemona
Returning to the Railroad HQ through fast travel, players will need to speak to Desdemona about their meeting with Patriot, and what they will need to advance the quest. Desdemona will tell the Sole Survivor to enter their report into PAM’s terminal, which is easily done by entering PAM’s room on the left of the Railroad HQ interior when facing the table and then selecting the Enter Institute Report prompt on the terminal itself. After this, PAM and Desdemona will be standing in this room and will discuss the next step, which is to access a password at the Cambridge Polymer Labs building.
Head To Cambridge Polymer Labs
Found to the left of the CIT Building, players can find the Cambridge Polymer Labs, a rather ominous building that hides a sinister truth. When arriving for the first time, players will be greeted by Molly, a Miss Nanny robot that will provide them with a job application. Following Molly will take them to the cleanroom, where they will be locked within this lab area until they complete a project.
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The Cambridge Polymer Labs is filled with feral ghouls, so it’s best to bring some ammo, some guns, and a few healing items and rad-aways. From this point on, players are going to be trapped within the Cambridge Polymer Labs, and they have to both find the password they are looking for, and search for a way out.
How To Escape Cambridge Polymer Labs
Luckily, this video will showcase how players can escape the Cambridge Polymer Labs without completing the experiment that Molly has demanded of them. Doing this will result in Molly and the automated turrets becoming hostile, but at the end of the quest, they would malfunction anyway. By doing this quest, players would receive the Piezonucleic Power Armor, but the main focus is to get the password for Underground Undercover and leave.
The password that players are looking for is within the laboratory’s second floor, so head up the stairs and go down the right corridor, where players will find a collapsed part of the ceiling they can walk up. Simply follow through the vents to drop down into a room with Dr. Will Bergman’s terminal. From this terminal, players will want to select Password Request (Archive) to unlock the password needed to continue the quest. With the password acquired and at the same terminal, players can override the lockdown by activating the Facility Defense System option. Players can escape this way, and return here at a later date to finish the experiment for the power armor piece.
Return To Desdemona
With the password acquired, players can head back to Desdemona at the Railroad HQ to show her the password. From here, and no matter what the player says, she will say that saving 13 Synths is not enough, and she is going to cut ties with Patriot, and instead use this opportunity to free as many Synths as possible. This will then send players back into the Institute once more, where they need to find and talk to Z1-14.
Give Liam The Password
Back where players first met with Patriot, AKA Liam, players need to head back here to give him the password. Once the password is safely in his hands, feel free to ignore him and continue on with the mission, as there is no more use for him, and no need to ask him any questions that may confuse him and his loyalties to freeing Synths, so simply do what he asks which is to update Z1-14 about the plan.
Talk To Z1-14
Discussing Desdemona’s plans with Z1-14 by the garden at the Bioscience Lab, he will agree and make preparations for the future, asking the Sole Survivor to speak to him again in 24 hours after he has spoken to his Synth brothers and sisters to see who would revolt against the Institute. Players can also offer to provide weapons to help them escape, but this is entirely optional and doesn’t aid much, still, players can leave weapons in a maintenance closet if they offer it. From here, players can either wait 24 hours within the Institute by sleeping, waiting on a seat, or roaming the Commonwealth for a day until Z1-14 is ready.
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After 24 hours and returning to Z1-14, he will state that the way forward is to eliminate some guards in a maintenance tunnel that can be found by the stairs between Synth Retention and Robotics. It’s a good idea to quicksave here because if things go wrong, the Sole Survivor is banished from the Institute and the mission fails.
Kill The Maintenance Guards
Inside the maintenance room, players will find around 5 guards. Usually, they are huddled in a corner, and players will want to dispatch them very quickly to avoid the innocent Synths from getting killed in the crossfire. It’s best to avoid explosives in that case, so instead, use a trusty weapon that deals a large amount of damage and begin taking the guards out. If the guards retreat, or players leave the area with hostiles, then they will fail their objective, so just be sure to kill them fast.
At this point in the quest, players have done all they can, and when they speak to Z1-14 for one more time, he will provide his thanks and tell the player that he needs time to prepare and that they should keep working with Father until they are ready to escape. Waiting is not based on in-game time, but the progression of some main quests, but doing so will make the Brotherhood of Steel and the Institute permanent enemies.
Continue Working With Father
In order to complete Underground Undercover, players must remain on the side of the Institute and complete their faction quests. This means players must complete the following quests whilst working with the Institute, and not betray them at any instance:
- The Battle of Bunker Hill
- Mankind – Redefined
- Mass Fusion
- Pinned
- Powering Up
- End of the Line – Avoid completing this quest, as it involves Father giving the Sole Survivor in order to eradicate the Railroad. Players should obtain this quest, but not complete it fully, and instead wait in the institute for a Synth to come to the player character and tell them to speak to Z1-14.
Speak To Z1-14 & Complete The Quest
After finding Z1-14, he will inform players that the Brotherhood of Steel has found the Railroad’s location, and time is of the essence to warn the Railroad and defend them. Players will need to head to the Railroad HQ straight away and speak to Desdemona, who will immediately complete the quest, pop the achievement, and begin Precipice of War.
Fallout 4
- Platform(s)
- PC , PS4 , PS5 , Xbox One , Xbox Series X , Xbox Series S
- Released
- November 10, 2015
- Developer(s)
- Bethesda
