Underground Undercover

Underground Undercover is a quest and achievement/trophy in Fallout 4.

Quick walkthrough
Infiltrate The Institute and meet with The Patriot.

Quest stages

 * 1) Talk with Tinker Tom
 * 2) Upload Encrypted message on any institute terminal
 * 3) Read Patriot's reply
 * 4) Meet Patriot
 * 5) Follow Liam
 * 6) Talk to Liam
 * 7) Talk to Desdemona
 * 8) Enter report on terminal
 * 9) Talk with PAM
 * 10) Get password for code defender
 * 11) Return to Desdemona
 * 12) Meet with Z1-14
 * 13) Give password to Liam Binet
 * 14) Give Z1-14 a day
 * 15) (Optional) Deposit weapons for rebels
 * 16) Kill tunnel guards
 * 17) Return to Z1-14
 * 18) Continue working for father
 * 19) Meet with Z1-14
 * 20) Warn Desdemona

Bugs

 * It is possible that Desdemona will not initiate dialogue when trying to warn her about the brotherhood.
 * This may be caused by Glory being dead. To fix go to Railroad HQ and use recycleactor 000508EE and 000508EE.moveto player in the console. There haven't been any reports of success with this fix though.
 * Try to load any save that the Sole Survivor didn't kill any Brotherhood of Steel in their base (The Prydwen, Boston Airport and Cambridge Police Station)
 * This bug can also occur if the player character has not killed any members of the Brotherhood of Steel in The Prydwen, Boston Airport, or the Cambridge Police Station, or if Glory is still alive.