The Elder Scrolls IV: Oblivion Guide - Thieves Guild
5: The Elven Maiden
Make a total of 100 gold selling stolen goods to one of the guild fences to unlock this quest. When you have sold at least 100 gold worth of stolen goods to Ongar the World-Weary in Bruma, speak to Armand in the Imperial City Waterfront when he appears at midnight and select the 'Thieves Guild Special Jobs' dialogue option.
You're tasked with stealing a bust of Llathasa Indarys in Cheydinhal. Travel to Cheydinhal and look for a beggar to talk to. For a small amount of gold, one of the beggars in the city will tell you where the bust is. You'll discover that the bust is in the Great Chapel of Arkay. Use your map to locate the chapel, and then step inside. Upon entering, proceed down the steps in front of you and turn right when you reach the bottom. Enter Sneak Mode, ensure that you are not being watched, and use a lockpick to unlock the door.
A guard is patrolling this chamber, so ensure that you have Sneak Mode toggled. Though it's dark and thus difficult to see, you should be able to find your way through while avoiding the guard. Go straight upon entering, hug the wall, and head down the passage that you come to on your right. Llathasa's Bust is straight ahead, so move up and take it into your inventory. Don't loot Llathasa's Tomb, as a ghost will appear and likely alert the guard to your presence.
Steal the bust of Llathasa Indarys from the Chapel Undercroft in Cheydinhal.
When you have the bust, take your time as you make your way out of the area, as the guard may be near. Once outside, you're home free. Too easy? There's more.
Return to the Imperial City Waterfront once you have the bust. The Imperial Watch are looking for Armand Christophe, apparently under the assumption that it was he who stole the Bust of Llathasa Indarys. Speak to one of your fellow guild members to learn that Methredhel is looking for you. Use the wait menu to pass one hour if you don't feel like waiting, and Methredhel should approach you.
Once Methredhel has explained the situation, you're tasked with planting the bust in Myvryna Arano's House. Locate Myvryna's home in the Waterfront, and toggle Sneak Mode in front of her locked door. She sleeps during the day, so use the wait menu to pass as many hours as necessary to make it 12:00PM before attempting to break in. Hieronymus Lex should be standing just a short ways away from Myvryna's front door. While in Sneak Mode, watch the eye icon on the screen; if the icon is bright and solid do not attempt to pick the lock, as this indicates that you are being watched. When the icon fades, that's your cue to pick the lock. You may want to create a separate save file before doing anything, just in case you make a mistake.
Plant Llathasa's Bust in Myvryna Arano's House in the Imperial City Waterfront and report to Hieronymus Lex.
Inside Myvryna's house, creep over to the cupboard next to her bed. Click on the cupboard to automatically place the Bust of Llathasa Indarys inside. Once the bust has been planted, head back outside and locate Hieronymus Lex. He won't believe you when you tell him that Myvryna is the thief unless his disposition is high enough, so play the persuasion mini-game or bribe him to raise his disposition to at least 70.
When Lex believes the story, follow him to Myvryna Arano's house. Watch the scene that takes place once inside, and then return to the Garden of Dareloth. When midnight arrives, Armand Christophe will appear as always. Speak to him to complete the quest. You can now use Dar Jee in Leyawiin as a fence.
Stealing Llathasa's Bust and planting it in Myvryna Arano's House.