Online:The Lady of Blood

Quick Walkthrough
#Find a way into Greymoor Keep.
#Free the prisoners.
#Search the library.
#Look for clues in the laboratory.
#Rescue Adusa-daro from Lady Essenia.
#Talk to Gwendis.

Detailed Walkthrough
Starting the Quest
thumb|right|Set the prisoners free
Near the east or western entrance of Greymoor Cavern, you will see a winded Dunmer woman named Relmerea Sethandus. She tells you that she's just escaped from the keep up ahead, and that she was told by the one who helped her escape to find someone named Gwendis. Relmerea is tired and afraid, and understandably wants to go home, so she asks you to find Gwendis in her stead. Head along the northwestern path through the cave until you reach a cliff overlooking a massive castle, where you'll find Gwendis. Gwendis and her sister, Adusa-daro, came to Blackreach to investigate the strange activity in Western Skyrim. Rumors of strange storms and powerful vampires drew them here to keep tabs on the situation.

The long and short of it is that Adusa entered Greymoor Keep and hasn't returned. Gwendis asks you to accompany her as she searches the keep for her missing friend. Vampires and their death hound companions guard the main entrance, and Gwendis wants to keep this investigation discreet, so you'll need to find another way in.

Find a Way into Greymoor Keep
Head through the courtyard to the northwest. When you hit the lamp-lined road, head east until you find a misshapen Orc named Grolag. He's terrified of you, and tells you about the castle. Greymoor Keep is home to Lady Essenia, a powerful and apparently very cruel vampire. Grolag calls you foolish when you ask for a way into the keep, but agrees to show you an alternate entrance. He runs down the road and points west, towards a cave. Head into the cave with Gwendis and enter Greymoor Keep's Undercroft. 

You can also head west instead of east and fight a weak vampire named Gatekeeper Malath. The scroll at his feet points you in the direction of the keep's undercroft.

Inside is what appears to be a laboratory or torture chamber of some sort. Navigate your way through the undercroft, and you'll reach the Keep's Kennels. Vampires of all stripes are being held captive in cages here. As you make your way through the prison, Gwendis calls for Adusa. One of the prisoners, Arlof, calls out to Gwendis, saying he might know where Adusa is. Unfortunately, he'll only tell you if you free him.

The First Roadblock and an Informant
Gwendis notices a balcony above Arlof's cage. There doesn't appear to be doors or gates on these cages, but the balcony might hold a switch or a button you can use to open them. Head up the stairs behind Arlof's cage, then head east. Flip the switch on the balcony, and the cages fly open, allowing all the prisoners to escape. Gwendis drags Arlof up the stairs and to the north to interrogate him. Arlof tells you all about Lady Essenia's experiments, and how she seeks to draw out the true might of vampires. Adusa was experimented on earlier, and weathered the torturous experience better than most of the other vampires. She was taken further into the keep. With this information in hand, you may now press forward to find Adusa. 

The Library
Navigate through the keep. Your next roadblock is in the library, where you'll find a locked door in a chamber with two thralls. If you speak to the thralls, they'll mention a visitor coming, that they need to tidy up lest they face punishment and that there's a "secret book" somewhere in the room. This "secret book" is a scroll on a side table to the right, titled Words of Entry. It contains a passphrase that can be used to enter Lady Essenia's laboratory: "We shall rise again." Start looking around the room for clues as how to enter the laboratory mentioned in the scroll.

The fate of test subjects which don't make the cut|thumb|right
The bookshelf containing "The Rebirth of the Blood Masters" is the one you want to activate. It is located in the southern portion of the room. Don't worry about reading every bookshelf; the bookshelves that could potentially open the door are labeled with the name of the book they always contain, and the activation prompt reads "Examine" as opposed to "Read". The door to the library appears in the back of the room, and you can now enter unimpeded.

The Laboratory
Traverse the laboratories until you enter Essenia's greenhouse. Start looking for clues as to what Essenia wants with Adusa. In a nook to the northwest lies Nonradil, a test subject attached to the walls via grasping roots. She tells you that Lady Essenia seeks to create bloodknights, which are powerful, perverse vampiric creatures. North of Nonradil lies a set of notes detailing precisely what Essenia wants from Adusa.

The fruits of her labor|thumb|right
The blood of Adusa's vampiric progenitor, Verandis Ravenwatch, is unique. Lady Essenia seeks to make full use of these properties, and potentially create a new form of vampirism that is even more potent than that of the oldest pure-bloods. However she means to achieve this, Adusa is undoubtedly in danger. Pass through the Cathedral of Blood and into the ritual chamber to stop Lady Essenia. You may have to kill Lady Essenia's bloodknight guard to cross the cathedral.

Stop Lady Essenia
Lady Essenia is performing a ritual on Adusa when you enter her chamber. Kill Lady Essenia, who uses a combination of vampire abilities, frost spells and very minor summons, such as the Burdening Eye and a shadowy clone. Just when you think the fight is over, a horriffic bout of shrieking rings out, and Lady Essenia is reborn as a monstrosity. Kill her a second time and talk to Adusa, who answers a few questions. Gwendis tells you to meet her outside as she takes care of Adusa. Speak with Gwendis in the spot you met her in outside Greymoor Keep. Adusa is sleeping peacefully, and Gwendis thanks you for your part in her rescue.
 

Bugs
 
A workaround is to locate the bookshelf left of the note on the table, just around the corner. Climb up onto the opposite bench and jump onto the top of the bookshelf. Fall down behind the bookshelf and the stone wall. You will now be trapped, but from here you can find and read the secret book from the back of the bookshelf and progress the quest. To get out from behind the bookshelf, you will need to fast travel out or use "get me unstuck" option.

As of 7/6/2020 for XBox, if you face the bookcase in first person,then go to Menu > Social > Emotes > Poses and Fidgets > Faint, the book will appear.

Quest Stages