Trigger: Speak to Desdemona
Reward: Railway Rifle, 100 Railway Spikes, 500 Bottlecaps, 600 XP
- There are two ways Underground Undercover can pop up in your quest log. The first is to seek out the Railroad for help during The Molecular Level, and having them assist you in creating the Signal Intercepter. You’ll receive this mission in the midst of that. Alternately, you can receive Underground Undercover after leaving the Institute and speaking to Desdemona about having infiltrated the place.
- Regardless, you’ll be sent to Tinker Tom. He’ll give you an Encrypted Message Holotape, with instructions to upload its contents onto any Institute terminal. There are plenty to choose from, some track one down, insert the Holotape, and read the message that follows. It will direct you to Institute Advanced Systems, specifically a storage room. (In truth it’s close to Institute Bioscience.)
- You’ll find Patriot waiting in this room. Chat with him a bit, then follow him to a Synth named Z1-14. Another chat follows. Speak to Patriot again and agree to help to continue the quest.
- Hop back to Railroad HQ and speak to Desdemona. That done, use P.A.M.’s terminal, next to where P.A.M. usually stands, to create a report about what you’ve found. Speak to P.A.M. once you’re done and she’ll send you off to Cambridge Polymer Labs, a location near Diamond City. It’s more or less across the street from the C.I.T. Ruins. We’ll deal with the Labs in this article, as they contains more than just the Bergman’s Password you’re looking for.
- Return to Railroad HQ and speak to Desdemona, then hop back to the Institute. You have two concurrent goals: give the Password to Patriot and speak to Z1. Despite how the story spins it, you still need to do both of these things to progress, so don’t hold back on handing over the Password. Both NPCs are in the same places you met them initially. That done, find a bed or a place to sit and wait for a day.
- Return to Z1 and he’ll ask you to take out some guards for him. You’ll find the elevator you need to access through a storage room in the south of the Institute. Another storage room waits at the top of the elevator shaft, and you’ll have to face off against four Synth Guards. You have the help of ally Synths, but they’re pretty terrible at combat, so take cover and use explosives. Your buddies go down often, but they can’t be killed. Leave after the Guards have been destroyed. It’s crucial you complete this quickly, as a prolonged firefight may lead to the Institute becoming hostile, ruining the mission.
- While speaking to Z1 you can also offer to leave weapons behind for the rebel Synths to use later in the game. You can drop them off in a storage box across from the room where you meet with Patriot. (I don’t know if this has a massive effect on the outcome, though it may give the Synths better weapons in later missions. Anyone know for certain? Let me know in the comments.)
- Return to Z1. He’ll confirm that all is well, ask that you not speak to Patriot again, and request you continue working with Father. This means completing several Institute quests, namely Synth Retention, The Battle of Bunker Hill, Mankind - Redefined, Mass Fusion, Pinned, and Powering Up. It sounds like a lot, but The Battle of Bunker Hill, Mankind - Redefined, Pinned, and Powering Up are all relatively short quests. It’s worth noting that proceeding with Mass Fusion on the side of the Institute will turn you into an enemy of the Brotherhood of Steel, and you’ll immediately fail any active Brotherhood quests.
- Upon completing the meeting in Powering Up a Synth will rush up and ask you to speak with Z1. You’ll find Z1 waiting in your quarters, and he’ll tell you to return to Railroad HQ. Speak to Desdemona to complete the quest, as well as jump right into the next one: Precipice of War. You're headed straight into combat with Brotherhood forces, so be prepared for lots of laser fire.