Typically, Amusei will be lingering around the area of the meeting place a few minutes before it starts.
Don't worry if Methredel steals the diary before you! See steps 8-9 above.
If you served time in jail and you follow the Mysterious Person who gives you the invitation note, she will lead you to merely a few feet away from the meeting place.
When you get there just pick the lock and you're in at the exact same time she is. Follow her and she will lead you directly to the house.
When Armand finishes giving instructions, Methredel instantly takes off running.
If you have trouble finding the meeting place, make it your active quest to get a map marker on the location.
Search it and you'll be the first to find the diary! There you will find a desk against the wall. Go directly to the far wall toward the right side of the room.
When in the house, here's your advantage: Methredel doesn't know where the diary is placed.
Armand Cristophe can sell you lockpicks for 5 gold each.
If all else fails, and Methredel makes it back to Christophe first, he will give you another task.
If you arrive too late and your opponent has already gotten it, you could either try to pickpocket him/her, or paralyze them and then pickpocket.
You may break into her house (in Waterfront District), open Methredel's Chest, take the diary and report back to Armand Cristophe.
If Methredel has the diary before you you can do only one thing: Steal it from her.
Open it, take the diary of Amantius Allectus and go to The Garden of Dareloth and report back to Armand Cristophe.
In the room you just entered you will find a desk.
Once you get there pick the lock and proceed into his house.
You may also give 10 coins to a beggar in order to let him mark on your map Amantius Allectus' House.
Go to Amantius Allectus House in the Temple District (follow Methredel once you fast travel).
Bring the diary of Amantius Allectus without killing him or Methredel or Amusei.
After a short introduction to The Thieves' Guild you will be told what your test is.
Then get a beggar's disposition above 70 and ask them about The Gray Fox.Choose the answer "I want to work with Hige:Join the Thieves' Guild in Oblivion Step 6.jpg|center|550px]]
Read a poster of The Gray Fox (can be found around the Imperial City), or ask for a rumor on The Gray Fox.
A Dark Elf will give you a mysterious letter she will say "take this, its from a friend".
Break a law (theft), go to jail and serve your sentence.