To be able to complete this you must first have completed every other main quest line in the Thieves' Guild and have the following achievement:
The Darkness Returns achievement in The Elder Scrolls V: Skyrim worth 15 pointsComplete "Darkness Returns"
In order to restore the Thieves' Guild to its former glory and assume the title of Guildmaster, you must perform 4 'special jobs' across four major Holds of Skyrim: Whiterun, Markarth, Windhelm, and Solitude.
In order to get a special job, you must first complete 5 smaller jobs in that hold. To get a job, talk to Delvin Mallory or Vex. The small job targets are randomized across the major holds and a tally of the small jobs is not visible to the player.
Jobs can be accepted and quit at will so if you have done all the jobs in a perticular hold select to quit the current job and ask for a new one (It can be the same style of job) untill you get the hold you need.
After completing 5 jobs in a particular Hold, Delvin Mallory will offer a Special Job in order to increase the Thieves' Guild influence in that Hold.
Once you have completed all four Special Jobs, it will start the 'Under New Management' quest. From here you can talk to Brynjolf to officially assume the title of Guildmaster but you will need to retrive you Thieves Guild armour so Do not sell it.
Delvin Mallory's Jobs:
The Bedlam Job - Steal enough items or gold to reach a given value within the specific Hold assigned. Can keep stolen items.
The Fishing Job - Pickpocket an item from a given character.
The Numbers Job - Modify the ledger book at a given business.
Vex's Jobs:
The Burglary Job - Steal an item from a house.
The Heist Job - Steal an item from a business.
The Shill Job - Plant a stolen item in someone's home.
The Sweep Job - Steal three items from a house.
Special Jobs:
Imitation Amnesty (Whiterun)
Objectives:
- Speak to Olfrid Battle-Born
- Steal the letter incriminating Arn
- Forge the prison registry
- Return to Olfrid Battle-Born Both in Dragonsreach
If you are Thane of Whiterun this is a simple fetch quest that can be completed in a couple of minutes.
Silver Lining (Markarth)
Delvin requests that you travel to Markarth to find a man with great influence in the city. Travel to Markarth and enter the first shop on your left from the front gate. This man will give you the initial quest.
You must retrieve a Silver mold from a group of bandits in Pinewatch shack just to the east of Falkreath. Once you enter the shack, go to the basem*nt. There is a note on the table that will tell you there is a hidden room behind the bookshelf. To the right of this bookshelf and behind the table is a small red button on the wall. When pressed, the bookshelf will open with a loud bang. Follow the caves hallways, kill all bandits, and when you enter the last room you will see the Silver mold on a table, along with some ore, potions and gold.
Also there is a stone of barenziah inside the dungeon before the sleeping bandit behind a locked door.
Summerset Shadows (Windhelm)
This quest really is a straight forward one: go to the bandit camp, kill their leader and retrieve the locket.
As you enter the tunnel system, you'll encounter a fork in the system where you can go either left or right. It is recommended that you take the right turn to avoid the 2 Thieves at the end of the system, unless you lack sufficient sneak skill in which case either turn will be fine to take.
The Locket is found on Linwe's corpse
The Dainty Sload (Solitude)
Speak to Erikur and he will ask you to "Put the Balmora Blue in Captain Volf's footlocker."
You can aquire the Balmora Blue in two ways: you can steal it, or you can buy it for 1,500 Gold. The safe containing the information about the balmora blue is in the bottom-most deck of the Red Wave (the ship where you get the Balmora Blue). You can either pick the lock of the safe (master) or pickpocket the NPC for it. The note reveals that "I stashed the Balmora Blue in a chest under the Wave. I put the best lock on it that money can buy." The chest is under the dock, just next to the Red Wave on the same side as the stairs leading on board, in the water (the lock is Expert).
From here get into the ship and plant the Balmora Blue.
Not everyone who wants to complete the Thieves Guild missions is playing a thief character. Some may be playing a heavy melee or magic class that doesn't have any sneak, pickpocket, speech or lockpicking skills raised or perks invested in those trees and just simply wish to complete these special jobs to be able to sell more treasure to a single merchant instead of lugging it around. It can be frustrating having to bounce between towns and merchants just to sell off the wide variety of valuable possessions that clutter the players inventory.
An easy way to acquire these special jobs, without using thief talents, is to do Delvin's Numbers Jobs or Vex's Shill Jobs. Numbers jobs are straight in and out quests that have the player running into a random business establishment in one of the holds and activating a business ledger that, in most cases, is sitting out of sight from anyone in the area. This makes doing the quest easy even for a non-thief.
Shill Jobs involve the player receiving a stolen item from Vex and planting it in a chest in someone's home or business.
