After you have fenced at least 1000 golds worth of stuff, Amusei will find you and tell you to go to Othrelo's House in the Elven Gardens district. As usual, Amusei will not look for you if you are already in that district, so be somewhere else for a while.
This is, without a doubt, a truly ultimate heist. You're going to break into the Imperial Palace and steal one of the Elder Scrolls. In order to accomplish this feat, you'll need the Boots of Springheel Jak and the Arrow of Extrication to get past some obstacles, although the Gray Fox doesn't know the nature of the obstacles. There are several tasks that you must complete before you can get your hands on one of the Elder Scrolls:
It's probably a bit much to remember, so he gives you a book that lays out the things you need to do. Blood Price is waived for this mission (you can kill anyone and everyone without retaliation from the Guild), but that doesn't mean that the guards won't put a bounty on you and the Palace is going to be swarming with them. Remember that the key to being a good thief is the ability to get in and out without anyone knowing that you're there. If you're careful, you won't have to worry about any of it.
You'll need to get into the Palace Basement. Waltz right in the front door (it's accessible to the public), hang a left and pick the lock at the end of the corridor. Like the ground floor, the basement is circular. You enter at one end of the circle. There is a patrolling guard in the basement, so your best bet is to remain stealthed until he passes you. Then either follow him around to the other end or cut through the center section (go right at the first opening). The Glass of Time is an oversized hourglass at the other end just activate it to unseal the Old Ways. Now get back out of there. You can unstealth once you're back up on the ground floor.
The entrance to the Old Ways is in the Palace Sewers. Just your luck, there isn't a sewer entrance in Green Emperor Way. So start in the Arboretum. It's just like the sewers when you started the game: rats, and mud crabs, mostly. As a good rule of thumb, when you come across a wheel that can be turned, turn it. Just pay attention to your map and compass marker and it will be difficult to get lost.
Your next stop is the sewers beneath the Arena Bloodworks. Now who do you think might find blood attractive? You got it - vampires. This area is not necessarily infested with them, but there are enough to where you'll want to tread cautiously. One thing that I've noticed is that there is at least one Cure Disease potion in almost every area where vampires are placed. So be sure you check out those boxes, crates and whatnot. If you're a good sneak and can get in a decent backstab, it may not be necessary, but it's always nice to have because there isn't any place down here to get diseases cured. Again, follow your compass marker, pay attention to your map and turn every wheel that you come across.
Eventually you'll reach the Palace Sewers. It's still Vampires, so be cautious. The entrance to the Old Ways is just a short hop from the second of two circular rooms (there are Slaughterfish in those rooms if you want to go fishing). Again, pay attention to your compass marker, watch your map and turn every wheel that you come across. (Back to Top)
The Old Ways are a lot like the area in the Tutorial dungeon before you got to the goblins. There may be a few rats, but mostly it's going to be levelled undead. It's a little confusing to work across because there are doors leading almost everywhere (pay particular note to the door marker for the Imperial Battlemage's Quarters - this is where you'll come out). Again, pay attention to your map and compass marker. Eventually you will reach The Lost Catacombs.
The Lost Catacombs
This is a fairly straighforward area, but it's important. First off, your way is blocked by a closed gate a little farther in. Secondly, there are some undead wandering in the area. Lastly, this is where the Boots of Springheel Jak come in. Look to your left and you'll see a set of stone steps that are only partially raised. After taking care of the undeads, put on the boots and jump up to the top of those steps. There is a button on the wall - push it. Now run around to the other side of the balcony area and push the other button (the Prima Guide says that you only need to push one - I haven't checked to see if it's correct). The way through is now open. In the back corner of this area is a sleeping pallet, if you need to rest. This is the only place in the whole quest where it's safe to sleep if you need to level up. Once you're ready to rock, proceed onward. There are two Dark Welkynd Stones just before the gate, but they've never fired at me. I don't know if this is because I habitually push both buttons, they were turned off prior to the game's release or I've just been one lucky stiff. Be cautious in any event.
The Hall of Epochs
This is essentially a two-area Ayleid ruin whose objective is to get you into the Imperial Place (yes, you're almost there).You can see two Dark Welkynd Stones flanking a pedestal on a raised walkway immediately in front of you. Move forward into the main chamber and dispose of the undead wandering around. Then go up the main staircase and look at the big statue. You'll get a journal entry about probably having to stand in a special spot in order to open the way. If you run over to where the Welkynd Stones are, you'll see two gates (one on each side) that are blocking your way to the pressure plate in front of the pedestal. Your task is to find the way to open those gates.
So head off to the right and unlock the gate leading to the next room. You'll come out on a balcony with a button to your left. Push it to open a secret door in the room below. Dispose of the undeads in the area and proceed into the next area (more undeads) and a second button in a crypt-looking room near the bottom. This button will open the gates and lower the walls that are blocking your way to the pressure plate. Now go back to the big chamber to find three leveled zombies and a leveled skeleton in the areas previously enclosed by the walls. The skeleton may turn out to be rather important if you didn't bring a bow to fire the Arrow of Extrication.
When you stand on the pressure plate, the big statue will turn around and a glowing keyhole will become visible. Your journal suggests taking a few practice shots before committing to using the Arrow of Extrication. If you didn't bring any spare arrows, the skeleton should have a few.
Your aim point is going to be near the hilt and crossguards of the statue's sword. For cryin' out loud, save the game before shooting. If you use practice arrows, you'll hear a distinctive "thunk" sound when you hit the keyhole. Once that happens, DO NOT MOVE YOUR MOUSE!!! Press <F2> to open your inventory, select the Arrow of Extrication and exit. Your aim point will not have moved. Just do a full draw and release and the Arrow should go right into the keyhole and open access to the door.
Don't get cocky yet. The two statues on either side of the big one have now come to life. The female statue (on the right of the big one) has Elven Armor and an Ayleid Longsword; the male statue (on the left) has Elven Armor and an Ayleid Mace. As soon as you get close, you'll hear the "shing" of a weapon being drawn. Both statues are equal to your level and it's not difficult to take them on one at a time. Sorry, you don't get to grab the weapons afterward.
After you dispose of the statues, check the time. Going through the door will put you into the Palace Guard Quarters (talk about out of the frying pan and into the fire). Again, the wee hours of the morning (2 or 3 a.m.) will work to your advantage because the guards will be snug in their beds. So wait, if necessary. When you enter, you'll come out in the fireplace. Each guard has a locked footlocker, which you're welcome to raid (it's stolen loot, though). Sneak through the common room and out into the hallway. Hang a left and sneak to the end of the hallway and the entrance to the Elder Scrolls Library.
There is going to be a patrolling guard, so find a dark corner in which to hide and wait for him to pass. The nice thing about this area is that there is a dark recess every few feet in both directions. Stealth is the watchword because these guys will not bother trying to arrest you. (Back to Top)
There is a patrolling guard in this area, too. Unlike the others, though, he's going to stop and pick up trash as he makes his rounds (there are several pieces of trash on the floor - researchers are such slobs). So just stay behind him until you reach the middle of the circle and pick the lock to get into the inner library.
When you enter the inner area, hang a right and sneak down to where you see a blind Priest sitting. There is a lever behind him. Pull it to open the door into the library proper. Now go all of the way around and sneak into the library (you're on the lower floor). There is a chair at the reading table in the middle of the room. Sit down and a priest will bring you an Elder Scroll. Take it and say nothing.
You've got the loot -- now it's time to get the hell out of Dodge. The way back is blocked. The door closed behind you and you can't get to the lever to open it. The only way left is up. If you feel that you need them, there are a couple of Chameleon scrolls and a Detect Life scroll in one of the bookcases. There are no skill books in this area, so don't waste time looking.
Do not, under any circumstances, talk to anyone. Just sneak up (you may have to stand aside to let a couple of priests get up and down the staircase) and go out the door at the top. Hang a left and go to the end to enter the Moth Priest quarters. There is a patrolling guard, but keep ducking into those shadowy niches as you work your way around to the Imperial Battlemage's quarters.
Once into Ocato's area (there is one patrolling guard), sneak your way into his personal quarters. You'll see a lot of display cases in the front half of the room. Aside from a few soul gems, 7 potions and an enchanted Battleaxe, there isn't anything else that's worth the risk of getting caught. Depending upon the time of day, you may encounter Evangeline Beanique, a Breton Battlemage equal to your level. She doesn't leave the area, but she will wander around the level if she's not eating or sleeping. Her Sneak skill is pretty low, so it shouldn't be too hard to get around/by her. But do keep in mind that she is a member of the Mages Guild, so plan on Daedra Hearts and Vampire Dust if you kill her. On the top shelf of the bookcase to the right of the fireplace is a skill book that will raise your Speechcraft. This is your only opportunity to get at it, so don't waste it unless the guards (or Evangeline) are hot on your trail.
Once you have picked up whatever you're going to pick up, activate the ash flue of the fireplace. You're in for a long fall. Equipping the Boots of Springheel Jak will protect you from most of the damage when you hit the sudden stop at the end, although it will destroy the boots. If you have a decently high Acrobatics skill and good Health points (or a Fortify Health potion/scroll/spell), you might be able to survive the fall on your own. In this case you get to keep the boots, but you will not be able to remove them from your inventory because they are still considered to be a quest object. It just depends on whether you think the extra 50 points of Acrobatics skill is worth it.
Now you're back down in the Old Ways, close to the sewer entrance. It's just a matter of working your way back out again. There are still a couple of vampires that you weren't able to take care of on the way in, so exercise caution and just follow your compass marker and map. The Southeast Tunnels will put you out on the shore of Lake Rumare if you don't feel like hiking back through the entire sewer experience.
Make your way back to Othrelo's House in the Elven Gardens district to deliver the Elder Scroll, receive the praise of your guildmaster and get a new task. This one is completely safe - no stealth or combat required. Deliver a ring to the Countess Millona Umbranox and tell her that a stranger sent it if she should ask. Report back on her reaction to it.
You won't have to worry about reporting back. If you deliver the ring in the audience hall, The Stranger will step forward and reveal himself to be her missing husband, Corvus Umbranox and the Gray Fox. He renounces his life of crime and gives Nocturnal's Cowl to you.
Nocturnal's Cowl, minus the "erased from history" part (the curse is broken now), fortifies your Sneak skill by 25 points, and gives you constant-effect Detect Life (120 feet) and a 200-point Feather. It still has some vestiges of the curse on it, though. Whenever you wear the cowl, you immediately acquire a 500 gold bounty (so wearing it around guards is not recommended) and a 100 Infamy. I've never had a guard offer to let me pay the fine - they all just go into attack mode. The Infamy is not a constant. Any crimes that you commit as the Gray Fox will increase that Infamy. So if you don the cowl and then complete the Dark Brotherhood's initiation quest, the Gray Fox's infamy will be 101. Those with their thinking caps on will see some potential here - let the Gray Fox take the heat for all of the Dark Brotherhood quests.
Additionally, you now have a guildhall. Go back to the Garden of Dareloth and you'll find a door into the main building. This brings you in to the basement of the guildhall. There is a common area on the ground floor and living quarters on the second floor. Armand Christophe will spend most of the day there and Fathis Ules will be there on a daily basis (no need to go track him down). All of the stuff that you stole for the guild is now upstairs, including Savilla's Stone (which doesn't actually do anything, but looks pretty neat).
Congratulations, guildmaster.