Underground Undercover is a main storyline mission for the Railroad faction in Fallout 4. It involves helping the Synths within the Institute organize a rebellion and escape.
Fallout 4 Walkthrough – Underground Undercover
This mission consists of many steps. We will now look at what you need to do to complete the Fallout 4 mission and claim your reward.
The quest begins once you have done all the work needed to create the teleporter to enter the Institute. Desdemona tells you about Patriot, the Railroad person in the Institute who helped the Railroad get the Synths out of the organization.
Talk to Tinker Tom and he will give you an encrypted holotape that you can upload to any terminal in the Institute to contact Patriot. Once you have it, step onto the teleporter pedestal to transport to the Institute.
