Oblivion:May the Best Thief Win

Quick Walkthrough
# Meet with Armand Christophe at midnight.
# Beat your competitors to Amantius Allectus' diary.
# Return the stolen diary to Armand.

Detailed Walkthrough	 
Once you have learned about the existence of the Thieves Guild, travel to the Garden of Dareloth and wait until midnight.

You will discover that three people have arrived in the garden. One is Armand Christophe, local Thieves Guild doyen, the other two are your fellow guild candidates, Amusei, an Argonian, and Methredhel, a Bosmer.

The Race for the Diary
Armand will inform you that in order to join the Thieves Guild, a simple competition will be conducted. You are to steal a diary from Amantius Allectus, and the first thief to retrieve the diary and return it to him will be inducted into the Guild.

Armand will only indicate that Amantius is located somewhere in the Imperial City, but that the local beggars might be able to tell you where his house is located. Amusei may loudly say that Amantius may live in the Elven Gardens District, but this is not true, so do not listen to him.

Plan of Attack
Once you have commenced the quest, Methredhel will begin to run towards the Imperial City – she appears to already know the target's location. You can opt to follow her, however she is quite fast and depending on your current level and speed you may lose her quickly.

By asking any of the Imperial City beggars (after a five-coin bribe), you will gain the information that Amantius lives in the far east side of the Temple District. The easiest beggar to query is Puny Ancus who is conveniently located just outside the Garden of Dareloth, directly behind Methredhel's shack. If his disposition toward you is high enough, he will tell you for free.
thumb|right|Amantius' diary details a grim experiment
With the location of Amantius' house confirmed, make your way to the Imperial City Temple District and enter the house.

You will generally find Methredhel already inside and sneaking around looking for the diary. As long as you head straight for the desk containing the diary quickly you should be able to obtain the diary before she does.

Creative Thieving
If you enter Amantius' house and Methredhel has beaten you and removed the diary already, you will be informed of this by a quest message. You will also be given a tip via the message that you will be able to steal the diary back from Methredhel (because neither you nor Methredhel is a member of the Guild yet, it's not considered a violation of Guild rules).

Methredhel will return to her shack in the Waterfront District and place the diary in a locked chest - where you can steal it while she sleeps. You may encounter Adanrel or Carwen awake inside which makes sneaking open her chest somewhat more difficult. You can choose to wait until the early evening, around 6pm, before attempting to steal the diary as Methredhel will be away from her shack for dinner. After 12-36 hours (a noon and then a midnight has passed since the diary was placed in the chest), she will retrieve the diary to deliver it to Armand. Alternatively, you can simply pick-pocket the diary from Methredhel on her way back home.

Welcome to the Thieves Guild
Return the diary at midnight to Armand in the Garden of Dareloth, and you'll have officially joined the Thieves Guild! If you complete the quest by giving Armand the diary, you will receive 1 Infamy point.

A Second Fighting Chance
If you do not manage to retrieve the diary and return it to Armand, you still have a chance at entering the Thieves Guild via a second thieving mission. Armand will instruct you to steal a sword from the shop A Fighting Chance, located in the Market District. Armand tells you that ''"Amusei is a bungler and won't get this offer," so there is no need to worry about competition this time around. Make sure you have lockpicks because you will need to break in some doors.

The sword, Rohssan's Antique Cutlass'', is located in a chest on the second floor of Rohssan's shop in her private quarters. Rohssan's unnamed dog is located in her private quarters, guarding the chest, so you will need to either:
Use your sneak or illusion skills to retrieve the sword without alerting the dog.
Kill the dog and retrieve the sword.
Use a Calm or Command Creature spell to pacify the dog after you steal the sword.

If you are attempting the theft at night, Rohssan is sleeping in her private quarters, so a sneak attack on the dog is best to prevent it from alerting her to your presence. Breaking into her quarters during the day while Rohssan is tending the shop is also an option, just ensure that you are successfully sneaking on the stairs when you pick the lock.

Return to Armand with the sword to become a member of the Thieves Guild and receive 2 Infamy points.

Blood Price
Killing either of the following NPCs while this quest is active will require you to pay a blood price to Armand:
Amantius Allectus
Rohssan

Notes
It is recommended that you start this quest at 1:00 AM. This will allow enough time for Amantius Allectus to get home and go upstairs to bed, allowing you to recover his diary without being seen by him.
The diary is not present until the quest begins, so breaking into Amantius' house beforehand will not help.
You can stock up on lockpicks from Armand Christophe.
If you try to pickpocket the diary from Methredhel while she is on her way from the house to her shack and a city guard catches you, it is possible for the quest to continue to point you in the direction of Amantius Allectus' desk in his house, even though the diary is no longer there. In this case you should ignore the quest marker and go to Methredhel's shack.
Strangely, after taking Amantius Allectus' diary, Methredhel will run into his basement. Following her will result in the quest being updated, and she will appear outside.
It is still theoretically possible to fail the second mission (retrieving Rohssan's sword). However, even if you are arrested, stolen quest items such as Rohssan's sword will be returned to you if you serve your time in jail (do not try to break out because it will not be in the evidence chest).
Armand's objective is to choose the most worthy contestant to join the Thieves Guild, but Methredhel ends up in the guild even if you win the initial challenge. Presumably, she is given the same second chance that is available to you. Amusei joins the Guild after the Lost Histories quest despite Armand calling him a "bungler".
Though Methredhel is supposed to be competing for a spot in the Thieves Guild, a copy of Followers of the Gray Fox will already be at the foot of her bed when you break in to retrieve the diary from her chest.
  An achievement will be unlocked upon completing this quest.
If you get a bounty when trying to get Amantius Allectus' diary, you will keep the diary if you pay the fine to the guard, and Armand Christophe will not comment about that when you give him the diary.

Bugs
 
 
 
 You can resolve this by locking the cell via the console command  , then leaving and giving Amusei at least a game day to return to the Waterfront.
Another more complicated method can also fix this. You will need a Command Humanoid spell, which you will cast on Amusei in the Leyawiin Dungeons and lead him out of the castle, you must cast the spell upon him every time you exit an area for Amusei's special nature dispels any spell effect every time a new cell is entered. You cannot fast travel, otherwise Amusei will just disappear again. This means you will have to lead him back to the Waterfront step by step from Leyawiin, which takes quite a long time. Once back at the Waterfront, take him to Dareloth's Garden and wait until Armand arrives while still keeping Amusei under command. When Armand arrives, wait for the command spell effect to wear off and talk to Armand about "Joining the Thieves Guild" and the quest should continue as normal.
 
 
 

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