This guide will help players complete the Railroad Quest: Underground Undercover in Fallout 4. Players must have completed and worked with the Railroad on the Main Quest: The Molecular Level for this quest to become available. Proceed with this quest to continue working for the Railroad faction.
If you were after help with any other areas of Fallout 4, then head over to our Fallout 4 guides walkthrough hub, featuring additional quest walkthroughs, as well as the locations for rare items like the X-01 Power Armor.
After having completed the Main Quest: The Molecular Level with help from the Railroad’s scientist, you should now have access to and from the Institute. It turns out there’s a guardian angel working from within the Institute that Desdemona wishes to contact. There’s just one problem: no one knows exactly who this guardian angel is. Agree to help Desdemona track down the Patriot, and report to Tinker Tom for further instructions.
How to Complete the Underground Undercover Quest
Talk with Tinker Tom
After speaking with Desdemona, talk to Tinker Tom about his method for contacting the Patriot. You will receive a Network Scanner Holotape encoded with a secret message. Your task is to travel to the Institute, and upload the encrypted message onto one of their terminals. With any luck, the Patriot will discover the message and post a reply.
Upload Encrypted Message on Any Institute Terminal
Travel to the Institute using the Relay on your Pip-Boy. Access one of the computer terminals, and insert the encoded Network Scanner Holotape. Select “Copy Encrypted Message” to upload the message to the terminal, then wait for a reply.
Read Patriot’s Reply, Meet with Patriot
In a few moments, Patriot will reply back with an encrypted message. Using the terminal, select the segment that reads “UrgentReply001” to see what they said.
Patriot has successfully received Tom’s encrypted message, and asks to meet you in the Advanced Systems maintenance room. Head the Advanced Systems division, and enter the side hallway to locate the maintenance room where Patriot is waiting.
Follow Liam, Talk with Liam
Introduce yourself to Liam, and speak with him about the message. Afterward, follow him through the Institute and get acquainted with a synth named Z1-14, who collaborates with Liam on his inside jobs. Z1-14 is unsure about your trustworthiness, however. If your Charisma is high enough, try to convince Z1-14 by saying that you’re fighting for synth freedom.
After meeting Z1-14, speak with Liam once again. Liam has been trying to rig the security system within C.I.T. to aid his rescue plan, but has run into some trouble. He requires a username and password to access an old pre-war security program, named Code Defender.
Talk to Desdemona
Head back to the Railroad HQ in the Old North Church to inform Desdemona of your progress. She tells you to consult PAM, but not before writing up a full report on your findings.
Enter Report on Terminal
Locate a room along the west wall containing a computer terminal and a robot standing nearby. Access the terminal, and select Enter Institute Report to input your findings.
Talk with PAM
PAM turns out to be the robot standing beside the terminal. Talk to PAM, and she will scan her database for viable credentials for Patriot to use.
How to Get the Password for Code Defender
PAM finds credentials for a user named Wilfred Bergman who had access to C.I.T.’s original system. To retrieve his credentials, you must first travel to Cambridge Polymer Labs just west of the C.I.T. ruins.
Upon entering the facility, you’ll encounter a robot named Molly who sets you up for orientation. Follow Molly on a guided tour of the lab, and watch out for Feral Ghouls. When you step into the clean room, prepare to be temporarily quarantined for your filthiness. Wait for the sequence to finish, then exit through the far door in the adjacent room.
Eliminate several Feral Ghouls as you head toward Lab C3 in the Mezzanine area. Enter through Lab C4, and locate a broken ceiling piece that forms a ramp leading up into the ceiling. Crawl through the ceiling crawlspace and drop down a hole leading to Lab C3. Or, if your Hacker perk is leveled high enough, simply hack the wall terminal just outside the lab door. Once inside, use the computer terminal on the desk to retrieve Bergman’s password. Then, access the facility defense system to override the security breach, allowing you to escape the lab.
Return to Desdemona
With the password for Code Defender in hand, return to the Railroad HQ and speak to Desdemona once more for further instructions. She has devised an even more risky rescue plan, but it is one that could save the remaining Institute synths. For now, just stick with the plan and bring the password to Patriot.
Give Password to Liam Binet
Use the Relay to teleport back to the Institute. Locate Patriot and give him the credentials to use on Code Defender.
Meet with Z1-14
Now locate Z1-14 in the atrium and inform him of Desdemona’s new plan. There will be a few persuasive dialogue options available to sway Z1-14 towards the Railroad’s cause. It’s best to keep Liam in the dark with this one, as the plan may not be in his best interests.
Give Z1-14 a Day
Z1-14 needs some time to mull over the new plans with his fellow synths. Wait for 24 hours, or return later after a full day has passed to see if he’s reached a decision.
Meet with Z1-14
- Optional: Deposit weapons for rebels
Return to the Institute after a full day and speak with Z1-14 once more. He was able to recruit a good number of volunteers for the cause, but all they need now are adequate weapons. There is a maintenance locker where you can optionally supply the volunteers with weapons for future use. Consider bringing extra firearms and items to this maintenance locker when you need to lighten your inventory carry weight.
Kill the Tunnel Guards
After speaking with Z1-14, locate a nearby storage room and ride the elevator to the lower tunnels. Eliminate all of the synth guards stationed at the tunnel entrance.
Return to Z1-14
Head back to the atrium to update Z1-14 of your progress and discuss the next steps of the plan.
Continue Working with Father
Keep working with Father by completing quests for the Institute to avoid raising suspicions. Proceed with the Institute Quests: Mankind Redefined and Mass Fusion.
Wait for Z1-14 to Contact You
Z1-14 needs extra time to iron out his side of the plan. After completing a couple more Institute quests, Z1-14 will contact you using a subtle message. Take the hint, and proceed to meet with Z1-14.
Meet with Z1-14
Head to your designated quarters within the Institute to rendezvous with Z1-14. He tells of a critical threat to the Railroad’s security, and urges you to inform Desdemona right away.
Return to the Railroad HQ to inform Desdemona of the threat, and to receive a new Railway Rifle perfect for the fight ahead. The next Railroad Quest: Precipice of War begins immediately after Desdemona mobilizes the Railroad’s defenses.