|The following is based on Creation Club content and is not canon.|
Listen to the faint radio signal to be directed to the Fens Way station. Navigate the area to a door to the subway maintenance access. Enter through a Novice locked door, and through one of two arched doors in the wall to find what appears to be an abandoned camp. Clear this section of the metro tube and continue back right to be ambushed by a feral ghoul who crawls out behind some scaffolding ramps and another feral who appears to be sleeping on a bed.
What remains of Wally Mack, who is now a glowing one, comes down from the top of the scaffolding ramps. Kill him and collect some interesting loot.
[verification overdue]When the Sole Survivor goes to Concord, one of two glitches can happen with this quest active. One, when the Sole Survivor exits onto the roof with the power armor and minigun, Concord does not have any raiders or the deathclaw boss, making it impossible to proceed with the quest to help Garvey and his wards. Or, the enemies are present, but after the Sole Survivor kills them, Preston Garvey and his wards do not complete their dialogue and do not go to Sanctuary. Either way, Garvey and his companions cannot go to Sanctuary. Bugs affecting Codsworth in Sanctuary are also possible.