How to unlock: From Whitechapel Charlie, a robot bartender, buy alcohol in The Third Rail in Goodneighbor (M6,4)
Once you buy any alcohol from Whitechapel Charlie, he will confess a secret to you. He tasks you with eliminating mafia bosses in three warehouses in Goodneighbor. You can haggle with him for better reward, using Charisma.
All three warehouses have been marked and they are within close proximity of each other. In each, there are a dozen-or-so opponents and they are most frequently armed with machine guns. To get into the warehouses, you need o pick locks (easy). After you have eliminated all of the enemies, return to the bartender for your reward.
Rewards for completing the quest: Experience points, 200-400 caps