Oblivion:Arrow of Extrication

Quick Walkthrough
# Wait for Amusei to find you, usually in the Imperial City.
# Go to the house of Malintus Ancrus in Chorrol and meet with the Gray Fox.
# Go to Bravil and talk to the beggars for information on Fathis Aren.
# Find and traverse the hidden passage from Fathis' room to his tower.
# Enter Fathis Aren's tower and steal the Arrow of Extrication.
# Go back to Ancrus' house in Chorrol and give the arrowhead to The Gray Fox.

Detailed Walkthrough
Orders
After you have fenced 700 gold and have completed the previous quest, Turning a Blind Eye, go to the Imperial City and wait for orders from the Gray Fox. Amusei should arrive shortly, and will give you orders to go to the house of Malintus Ancrus in Chorrol. You meet the Gray Fox once more, and he will tell you that you need to steal the Arrow of Extrication from the Court Wizard of Bravil, Fathis Aren. Once in Bravil, pay a beggar who tells you about Fathis Aren. You find out that Fathis keeps his most treasured items in a ruined tower outside of town. There may also be a secret passage from the castle to this tower.

The Castle
Head to the Castle in Bravil. Fathis' room is in the North Wing of the Castle. Getting into the North Wing might be tricky if you don't time it right, so wait until early morning when the guards change shifts, around 7:30am, to pick the lock and enter. Enter the chamber and look for the Arrow. More specifically, you only need to check the two chests that are to your left as you enter. Unfortunately, the arrow is not in either. You will then get a journal entry telling you to look for a secret passageway. One of the two pillars on the alcove straight across from the entrance of Fathis' room is the lever that opens up the secret passage to Bravil Wizard's Grotto. If you are in the Mages Guild, note that you can get kicked out for stealing items in this room.

Passage to the Tower
Bravil Wizard's Grotto and the subsequent Bravil Wizard's Lair are unusual dungeons, where you will encounter Conjurers, Dremora, and possibly Daedric creatures. There are several locked chests worth opening, and useful alchemical ingredients can be found in many places. Moving through the dungeon will also require unlocking some gates and doors, so bring your lockpicks.  

As you explore, you will eventually find a door that says it needs a key to be unlocked. The only key to open this door is Aren's Strange Key, which is carried by Fathis Aren; you may pickpocket this key from him ahead of time if you wish. If you don't have the Strange Key, you will need to take the underwater passage found in the tunnel system. The underwater tunnel is quite deep, and traversing to the bottom will reveal the unique Giant Slaughterfish boss and a door leading out to the bottom of Niben Bay. However, the tunnel to the next zone is only partway down the cavern, and it is quite tricky to find. Of course, water breathing spells/potions will be helpful in navigating this area. For more information on these zones, see the place page.

Fathis Aren's Tower
In order to get out of the fort area, you need to take the arrowhead and Fathis' key from his chest, which is located in the same room as his lab is set up. The chest is unowned, so taking anything from it does not count as stealing. Most other things in the tower are marked as Fathis' property, however, and he will not be happy if you take them. To make matters more complicated, if he sees you, unless your disposition with him is 95 or higher, he will likely attack you on sight. If his disposition is higher than 95, you can easily walk past him to access the quest-related chest. Members of the Mages Guild need to be particularly careful not to be caught, as they will be expelled from the guild if they are. Higher ranked mages are likely to have an easier time taking the arrow since their allegiance with the Mages Guild will raise Fathis' disposition. Finally, if you kill Fathis during this stage, you will not incur the blood price, but you will get kicked out of the Mages Guild.

Afterwards, make your way outside using the main door and return to the Gray Fox who will reward you with 500 gold and promote you to Master Thief. He will also tell you that you can now use Fathis Ules, the best fence in the guild, as your fence. Unfortunately, due to a bug, Fathis will not offer his services after completing the quest Sins of the Father, even if you returned the Honorblade of Chorrol to him. However, you can still invest in Fathis Ules as long as you are an Expert in Mercantile.

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

Notes
Amusei will not seek you out and initiate the quest if you are in jail or in the Dark Brotherhood Sanctuary.
  An achievement will be unlocked upon being promoted to Master Thief.
Fathis will always be at the alchemy station in his tower during the later parts of this quest; he will never eat, sleep or wander at any time, no matter how much time passes. He only breaks this schedule if you engage him in combat.
You can sometimes find Fathis on the road just west of Bravil as he is out travelling.}  You may, at this point, kill him or pickpocket his Tower Key from him, and walk in through the front door of his tower. Note that killing him at this point will require you to pay the blood price, and he may be hostile towards you if you become detected depending on his disposition.

Bugs
 
 
 
 
  You can fix this with the console command   (toggle collision) to enable you to pass through the wall.
 
 
If this happens, go inside and talk to Malintus before speaking with the Gray Fox, otherwise the Independent Thievery quest will not update and you will not be able to start the next quest.
Alternatively, you can fence your amount up to the next benchmark or attack the Gray Fox and make him follow you out of Malintus Ancrus' house. This seems to fix the journal.
Another option is to wait until the early morning, then enter the house. If Malintus is asleep, talk to the Gray Fox and complete the quest. Exit the house, and when the door icon turns red, reenter. Malintus should light a torch and approach you. Quickly exit again, and Malintus should exit the house and your journal will update. If he does not appear after a few seconds, reenter and instantly exit again.
 
 
 
  The following console commands can be used to advance:  ,   and  .

Journal Entries