Morrowind:The Code Book

Quick Walkthrough
# Talk to Eydis Fire-Eye about orders.
# Retrieve the code book from Sottilde.
# Return to Eydis Fire-Eye for your reward.

Detailed Walkthrough
The Code Book
Eydis Fire-Eye in the Balmora Guild of Fighters asks you to retrieve a code book currently held by Sottilde at the South Wall Cornerclub in Balmora. If you check with Percius Mercius he'll tell you that the mission seems okay but that you should try to avoid killing Sottilde. He calls her a "pushover" and suggests you talk her into handing it over.

Confronting Sottilde
Sottilde is just inside the Cornerclub entrance.  Her response to your inquiry about the code book -- as well as your choices on how to acquire it -- will depend upon the factions that you belong to:
If you are not a member of the Thieves Guild, Sottilde will refuse to give you the code book right away.  In fact, she may deny even having it. You have two choices:
Increase her disposition above 70, and she should give you the book.
Taunt her until she attacks you.  You can kill her, grab the code book, and get away without incurring a bounty.

If you are a member of the Thieves Guild, she will refuse to hand it over regardless of her disposition (raising it to 100 or lowering it to zero does not matter). Again, you have two choices:
Kill her. You can use Taunt or Frenzy to trigger her into attacking you so you don't get a bounty, or you can just plain kill her, but you will be expelled from the Thieves Guild and gain a bounty.  If you can kill her without being detected, you will not be expelled and can loot it from her body.
Steal the book.  Find a spot where the other characters can't see you picking her pocket.  Using  Chameleon will help avoid being caught while doing so.

Return the Book to Eydis
Once you have the book, return to Eydis for an increase in faction reputation, and 50 drakes.

Notes
You will not receive this quest if you complete the Thieves Guild Bitter Cup quest prior to receiving this quest from Eydis. However, completing the quest includes going back to Gentleman Jim and announcing that you have completed the quest. If this quest is next up from Eydis and you give her the Bitter Cup, then ask for a new quest without first reporting to Jim, you will still get the quest. If you accept this quest before completing the Bitter Cup, then completing the Bitter Cup will allow you to bypass this quest by asking Eydis for more Orders, after which she will give you another quest. 
If you're in the Thieves Guild, Sottilde will tell you that the Camonna Tong and the Fighters Guild have certain ties.
A chat with Percius Mercius in the Ald'ruhn Fighters Guild will tell you Sottilde is a pushover, and you will be encouraged to try not to kill her, which gives a clue as to how to obtain the book: it can be pickpocketed off her if your skill is high enough (and if you can remain undetected).
If you aren't a member of the Thieves Guild, and you return the book to Eydis Fire-Eye immediately after taking it from Sottilde, then you will not be allowed to join them after performing this quest. This is because this particular quest is the first of several turning points between the Thieves Guild and the Fighters Guild, and it forces you to decide whose side you're on right then and there. Unfortunately, you cannot just simply take sides with both factions if you're already a member of both, unless you exploit a certain loophole. Join the Fighters Guild, and when you get this quest, get Sottilde to give you the book, and then talk to Sugar-Lips Habasi about membership for the Thieves Guild. Now that you're a member, they won't be so hostile towards you after turning the book over to Eydis Fire-Eye. You can also skip this quest, and the remaining quests by Eydis Fire-Eye, and still get to be the head of both guilds by doing other quests.
You can complete this quest and stay friendly with both factions by taunting Sottilde into attacking you. Additionally, you can stay friendly with both factions by simply pickpocketing the book from Sottilde, provided that you are not detected. This is the ideal way to complete the quest as a member of the Thieves Guild, as your disposition will not decrease with either faction.
If a frenzy spell is cast on her to increase her Fight (i.e., its inclination to attack), then it might not be necessary to taunt her. Additionally, a frenzy spell of magnitude 100 is relatively cheap and easy to cast due to the small base cost of Frenzy.
Each time you refuse to give the book to Eydis, her disposition drops by 5.

Bugs
 

Quest Stages