A Knife in the Dark

Background
As a result of your innocent murder, and as a test of your loyalty to the Dark Brotherhood, Lucien Lachance asks you to kill Rufio in the Inn of Ill Omen.

Walkthrough
To begin the quest, you have to kill a innocent NPC. When you do this a message will appear on the screen saying "Your actions have been observed by forces unknown." The next time you sleep in any bed, Lucien Lachance will approch you and say that your invited to the Dark Brotherhood and to join you would have to kill Rufio in the Inn of Ill Omen. Reaching the Inn is the most difficult part of the quest, but that isn't saying much. Simply set off from the nearest mapped location (this varies depending on how thoroughly you have explored the game) and enter the inn. There are normally a number of people on the ground floor, but you need not concern yourself with them. The target, Rufio, is downstairs in his room, so take the trapdoor (near the front door) to the lower floor and kill him in his sleep. Using the Blade of Woe, or any other weapon, will kill Rufio instantly.

If you wake him and try to talk to him first, he'll deny that he did anything. If you say, "Oh, but you have, Rufio," Rufio will plead that he "didn't mean to do it...She struggled!" Apparently he killed a woman and he "had to do it." He may also run away from you and try to hide in the other room on this floor, cowering beside the bed. It does not seem possible to induce him to attack you with Frenzy spells so as to avoid the Infamy from murdering him.

With the target slain, you need only fall asleep again to meet once more with Lucien. You may sleep in Rufio's bed as it is the quickest way to achieve this. Once finished talking to him, you have completed the quest and been admitted into the Brotherhood.

Lucien will tell you head to the Cheydinhal Dark Brotherhood Sanctuary. Go to the Abandoned House in Cheydinhal, enter through the front door, then go into the basement. Knock on the door inside and say "Sanguine, my Brother" when asked a question. Enter and talk to Ocheeva.

Farming the sneak skill
Rufio's room makes for the perfect location to level up your sneak skill quickly. Merely take off any boots you have on and sneak continuously into the corner made between the wall and his bed.

Destroying the Brotherhood's link
If you joined the guild by mistake and don't wish to join it, there is a way to leave the guild. After going to sleep and waking up, Lucien Lachance should appear next to you, go talk to him. Now quickly swipe him, as he turns invisible and starts walking away. He should then start attacking you. He can be a problem to lower level characters, but if you have powerful weapons and some potions, or you attacked him in a crowded area, this should be easier. Once he is dead, you will get a journal entry (see below) that tells you that it is now impossible to join the guild. This also means that you are unable to obtain any rewards given in the Dark Brotherhood, such as the spells given/sold to you and unique items, the Summon Rufio's Ghost scroll and Shadowmere. It is recommended to pause the game after you finish speaking with Lachance or save before you sleep to meet him to decide whether you want to leave the guild and miss out on the bonuses or not.

Journal entries
Upon receiving the quest:
 * While sleeping, I was visited by Lucien Lachance, a representative for the assassins guild known as the Dark Brotherhood. He said that if I wish to join his "family," I must go to the Inn of Ill Omen, find a man named Rufio, and kill him. If I simply leave Rufio alone, Lachance will never visit me again.

After killing Rufio:
 * The man named Rufio is dead. The next time I sleep in a location he deems secure, Lucien Lachance will visit me once more, and complete my entrance into the Dark Brotherhood.

After speaking to Lucien:
 * I must now go to the abandoned house in the city of Cheydinhal, and attempt to open the door in the basement. When questioned, I must answer with "Sanguine, my Brother" to gain access to the secret Dark Brotherhood Sanctuary. Once inside, I should speak with Ocheeva.

After entering the sanctuary:
 * I have gained entrance into the Dark Brotherhood Sanctuary. I must now speak with Ocheeva.

After speaking with Ocheeva:
 * I have spoken with Ocheeva.

If you murdered Lucien Lachance:
 * Lucien Lachance, the Dark Brotherhood's representative, has been killed. He was my link to the mysterious assassins guild, and now that link has been severed... forever.