Darkness Returns

Objectives

 * Enter the Twilight Sepulcher
 * Speak to the Nightingale Sentinel
 * Follow the Pilgrim's Path
 * (Optional) Retrieve Nystrom's Journal
 * Return the Skeleton Key to Ebonmere
 * Listen to Nocturnal
 * Speak to Karliah
 * Choose Nightingale Role

Walkthrough
You must take the Pilgrim's Path to the Twilight Sepulcher in order to put the Skeleton Key back where it belongs. As you enter the Sepulcher, you stumble upon the ghost of Gallus Desidenius, the Nightingale murdered by Mercer Frey. He warns you that, because the Key is missing, the other ghosts have been corrupted and are now hostile to you. When asked about the trials ahead of you in order to reach the Ebonmere Lock, he advises you to look for a journal that belonged to Nystrom. His skeleton is to your left as you look at Gallus.

Nystrom's journal holds some clues to the trials:

"Shadows of their former selves, sentinels of the dark. They wander ever more and deal swift death to defilers

"Above all they stand, vigilance everlasting. Beholden the murk yet contentious of the glow."

"Offer what She desires most, but reject the material. For her greatest want is that which cannot be seen, felt or carried."

"Direct and yet indirect. The path to salvation a route of cunning with fortune betraying the foolish."

"The journey is complete, the Empress's embrace awaits the fallen. Hesitate not if you wish to gift her your eternal devotion."

Nystrom also says that the man who gave him the clues "mumbled nonsensical phrases like "night is the new day" and how he was the "ghost of the sun"."

For the first trial, you face the shadows of their former selves, sentinels of the dark - Nightingale ghosts, hostile and powerful. You can either sneak past or kill them.

For the second trial, night is the new day: avoid the light and stay on the darkest path. Sprinting and using Whirlwind shout will make it easier.

For the third trial, In the room with the statue and a dead bandit lying in front of it, there are two sconces to either side of the statue. To the left of the left hand sconce there is a chain, and at the right hand side of the right sconce there is a second chain. Pull the two chains to open the door behind the statue.

For the fourth trial, avoid the traps: watch your step and use Whirlwind Sprint or Become Ethereal. Be careful with the doors. Before you find the first trap, there is a locked iron door to your left that can be used to avoid the traps, but you may be seen by ghosts (in the pit to the left are 2 skill books: Proper Lock Design and Sacred Witness). The swinging axes can inflict diseases upon you, even if you are a werewolf.

Enter the Twilight Sepulcher Inner Sanctum, fall into the pit and search Anders' skeleton; read the message. Wait a few seconds until the Skeleton Key reacts. The ground will disappear and you will return the Skeleton Key to the Ebonmere Lock. You will summon Nocturnal, who will bid you to drink from the Ebonmere, "for this is where the Agent of Nocturnal is born".

You must then speak to Karliah, and she explains to you the choice you must make between the Agent of Strife, Subterfuge and Shadow. To pick one, you must simply step on the corresponding moon. They give you greater Powers, usable once a day. After you speak to Karliah, Gallus' ghost will appear and they will speak shortly before he goes to the Evergloam. Karliah, then, goes back to Nightingale Hall.

Powers
Shadowcloak of Stealth
 * The crescent moon represents this power, which makes the player the master of remaining unseen. Once a day you can become invisible whenever you crouch for 120 seconds, much like the Shadow Stone.

Nightingale Subterfuge
 * The half moon represents this power, which allows the player to utilize shadow to cloud the judgment of those around them. Once a day, you can activate it for 30 seconds in order to make people and creatures on the spell's area of effect attack anyone nearby.

Nightingale Strife
 * The full moon represents this power, which, when used, instantly absorbs 100 Health points from the target. This power can also be used once a day.

Bugs

 * If the character leaves the Twilight Sepulcher and returns, the door behind Gallus may be blocked thus making it impossible to finish Darkness Returns. Using the console command "coc twilightsepulcher02" will transport the character directly to the inner sanctum successfully bypassing the immovable door behind Gallus.
 * Same as above but if you are on a console, look to the right of the door against the wall you will see a gap between the wall and the door where you can fall under the map. take a running jump to get to the ground on the other side of the door.
 * NOTE: If you miss the jump then you will die and have to try again, so save before you try it.
 * Near the end of the quest after Nocturnal bids the player farewell and returns back into the well, the quest marker will get stuck in the ground and Karliah doesn't come to speak with the player. This leaves the player stuck in this room for eternity, even after many reloaded saves the same result occurs. To solve this problem on PC, bring up the console with "~" after Nocturnal goes into the well and type "setstage TG09 60" which will set the "Listen to Nocturnal" part of the quest to complete and activate "Speak to Karliah." Then, bring up the console again and type "prid 00058F1A" then press enter and then type "moveto player" This should bring Karliah to the player and make her able to be talked to. (If that doesn't work try with: spawn Karliah with player.placeatme 1B07F. When Nocturnal is finished, you may need to update the quest with setstage TG09 60 )
 * This bug may be fixable by using the Wait button to wait for 24 hours.
 * Waiting for an hour also appears to work.
 * Trying this fix on PS3 results in the quest updating to * Speak to Karliah, by now clicking several times on her you might get her attention and be able to finish the quest.
 * A fix for this bug is to uninstall the game install then reload a save before falling down into well. Karliah will still dissapear before Nocternal appears but with the wait for 24 hours fix, she will appear again. It is important at this stage to speak to her before she goes through the door.
 * A weird fix is to reload your save before falling into the pit. (Make sure you have any weapon sheathed and not crouching). After falling through the bottom and using the key, Karliah will appear to be walking out one of the doors. Try and stop or delay her by walking in front of her. The quest should continue on its own, but you may have to let Karliah by before Nocturnal finishes her speech.
 * Try bringing up the console with "~" after Nocturnal goes into the well and typing "setstage TG09 60" which will set the "Listen to Nocturnal" part of the quest to complete and activate "Speak to Karliah." Then, bring up the console again and type "prid 00058F1A" then press enter and then type "moveto player" and press enter again. This should bring Karliah to the player and make her able to be talked to.
 * Same as above but Karliah is actually invisible. And you can talk and leave.
 * Same as above but Karliah leaves before Nocturnal finishes speaking. Eternal wait, unable to be stopped with reloading saves
 * Just before biding goodbye, if the player (is rude) and tab ends the conversation, Nocturnal may bug out and be interactive while in the ground. This may turn her into a follower or aggressive guard in terms of speech options.
 * When the player puts the key into the lock there's a chance Karliah may enter the blue portal before you speak with her rendering you unable to proceed with the quest.
 * I got it to work by standing on the side Karliah comes in put the key in then back up to the door she stops and looks at you, then the quest went straight on after Nocturnal got done talking.
 * I waited 24 Hours then Karliah reappears to then talk to you to receive Nocturnal Ability and finish the Quest
 * A possible solution is to use the console command "kill" on Karliah to stop her from moving about and use "resurrect" to progress (PC)
 * I waited an hour, then spam talked Karliah, that seems to work, if you can get it before she dissapears
 * One way to get around the glitch here is to wait until Nocturnal has finished her speech and goes into the void, Once she has gone then open the console with the ~ key and type: placeatme 0001B07F. This will place Karliah beside you and allow you to finish the quest.
 * Once the player has reached the Inner Sanctum and speaks with the manifested Nocturnal, she departs and the player is directed to speak to Karliah, who has appeared in the room, in order to proceed. When approached, Karliah will simply say "Yes, fellow Nightingale?", making it impossible to complete the quest and impossible to leave the room.
 * This bug occurs when, upon completion of "Darknes Returns", the Player does not earn the achievement for returning the Thieve's Guild back to its former glory. No current fix.
 * Temporary fix for PC, use console command "setstage TG09 70". You won't be able to listen to any of her dialogue but you can immediately choose one of the three moons to stand on, then the action proceeds as normal.
 * Currently, there is no fix for this bug. Reloading, waiting and diverse player positioning in the Sanctum have no effect. Fixed this problem by reloading a save prior to (accidentally) finishing Hard Answers twice. Sometimes if you go into the Dwemer Museum after having already completed Hard Answers, Hard Answers will load up a second time. I believe this is the cause of the glitch because Bryjnyolf also mysteriosly disappeared from the guild after the 2nd Hard Answers. Go back prior to this if you can and hopefully you'll be fine.
 * This glitch is caused by a seperate glitch in which you complete the quest Hard Answers twice. In order to get around this glitch, reload to a save before you completed Hard Answers a second time and complete Darkness Returns.