Underground

The Underground is the largest criminal organization, located in the Downtown district of the Hub. The Underground's hideout, or Decker's Underground, is located underneath the Maltese Falcon.

Members
Decker is the head of the Underground, and never leaves the hideout (most likely not to risk being captured by the Hub Police). Your ability to speak with him is granted only by his door guard Kane, and even so, you will never be able to speak with him without Kane guiding you, and taking you directly back, removing the ability to enter the hideout without entering combat. Decker is considered the largest threat to the Hub and merchants who aren't willing to cooperate.

Next to the bartender is a room guarded by Kane, a minion of the Underground and possibly Decker's right hand. Kane makes sure only people Decker wants to see are let in, and handles all of his payments. Kane is recognizable as a very powerful and durable opponent.

Inside the hideout there are five other guards or members who protect and do business for Decker, but you can't speak with any of them, and they aren't given names. Other members could thrive throughout the streets of the Hub, but you wouldn't be able to tell.

Affiliates
The Friendly Lending Company, or the FLC, is a separate criminal loan shark company in the Downtown district, thus inevitably cooperates with the Underground. Lorenzo Giovanni, the owner of the FLC, never comments on affiliation with Decker (likely to maintain a positive appearance), but one of his guards, Avery, can be found fighting for the Underground when they are attacked by the Hub Police.

In the Dispose of merchant quest, Decker asks that the Vault Dweller kills both Daren Hightower and his wife due to their lack of cooperation. This suggests that all the major companies in the Hub cooperate with the Underground, considering Decker never asks for their extermination.

Quests

 * If Decker finds you suitable, he triggers the Dispose of merchant quest and asks that Daren Hightower and his wife in the Heights be exterminated. To exterminate them, you will have to fight off all of Hightower's guards as well.
 * Once you've completed the first quest Decker will trigger the Dispose of Jain quest and asks that Jain of the Children of the Cathedral be killed, which likewise will make it necessary to attack her two guards and Thorndyke the Healer.
 * As long as one of these quests is triggered you can go to Sheriff Greene in the Downtown Police Station and alert him of a crime. He will ask you to join the Hub Police in taking down Decker and the Underground. This quest will not be marked in your PipBoy.