The Elder Scrolls IV: Oblivion Guide - Main Quest Walkthrough
After speaking to Martin about the Mysterium Xarxes, he tells you to speak with Jauffre about the Mythic Dawn agents spying on Cloud Ruler Temple. Set 'Spies' as your active quest, and follow the active quest marker on your compass to locate Jauffre. Select 'Spies' from the list of dialogue options while speaking to Jauffre. He tells you that strangers have been sighted near Cloud Ruler Temple. He suspects they are Mythic Dawn spies, based in Bruma. Jauffre suggests speaking to Captain Burd in Bruma about any strangers in town.
Captain Steffan has additional information regarding the spies. Follow the active quest marker on your compass to locate Captain Steffan and speak to him. He tells you that the spies have been spotted on the road to Cloud Ruler Temple, usually near the rune stone at dusk.
Leave Cloud Ruler Temple and follow the green marker on your compass to reach the Hestra Rune Stone. According to Captain Steffan, the spies have been spotted near the rune stone at dusk. They should turn up at around 10:00PM, so press the Back/Select button and wait the number of hours required for it be that time.
Look for the Mythic Dawn spies at the Hestra Rune Stone southeast of Cloud Ruler Temple at around 10:00PM.
The spies will immediately cast a spell to summon armour and attack upon spotting you. Take out the spies, and then search Jearl's corpse and remove Jearl's Key and the Basement Key from his inventory. The next person you need to see is Captain Burd in Bruma. Fast travel to Bruma and follow the active quest marker on your compass to locate him. He is most likely in Castle Bruma. Select the 'Spies' dialogue option while speaking to Captain Burd. Inform him that Jearl was a spy to receive permission to search her house to look for clues.
Locate Jearl's house, which is marked by the red active quest marker on your compass, and head inside to investigate. There isn't any apparent evidence upstairs, but there is a trap door by the table that leads down to the basement. Scour the basement for a document entitled 'Jearl's Orders,' as well as copies of the first two volumes of the Mythic Dawn Commentaries. Once you have the document, head back upstairs. Exit Jearl's house and fast travel back to Cloud Ruler Temple.
Retrieve the Jearl's Orders document from Jearl's home in Bruma.
Present the document to Jauffre to complete the quest.