- Kill 15 City Guards or 3 citizens.
- Travel to the location specified upon receiving the letter.
- Talk to the alchemist in the specified apothecary to receive the poison.
- Travel to the next specified location and enter the target's residence.
- Take the decanter and drop it.
- Travel to the next specified location and talk to the contact to complete the quest.
To activate the quest, three citizens or fifteen guards must be murdered. Upon doing so, the Hero will receive a letter from the Dark Brotherhood claiming that they must join them or else they will hunt the Hero down. Travel to the location specified in the letter, and meet with the city's alchemist to receive the poison.
Travel to the location the alchemist mentioned, and enter the targets residence. Citizens can be asked for the location of the residence if it is currently unknown to the Hero. Upon entering, find and pick up the decanter and wait for a message to pop up. Upon receiving the message claiming that the poison has been added, drop the decanter and leave the residence.
Travel to the next location specified by the alchemist, and locate the contact's residence. Upon speaking to the contact, the quest will be completed and the Hero will gain membership into the Dark Brotherhood.
If the Hero does not complete the quest within a specified time limit, the Dark Brotherhood will hunt them down as they do not accept "rogue killers."