Skyrim:Beyond Death

Quick Walkthrough
# Locate Valerica.
# Kill the Boneyard Keepers.
# Follow Valerica.
# Slay Durnehviir.
# Retrieve the Elder Scroll.
# (If not a vampire) Retrieve the Soul Essence Gem. (Misc. objective)

Detailed Walkthrough
thumb|right|Skyrim:Serana|Serana fighting a Keeper
Upon your arrival in the Soul Cairn, follow your quest marker to the Boneyard and find Serana's mother Valerica standing near the entrance. While you are able to speak with her, she cannot be reached due to an invisible barrier. During the course of interacting with her, she will reveal that the barrier can only be removed by defeating the three Boneyard Keepers.

The Keepers each live in separate towers, apart from the main Boneyard.  The quest markers will lead to all three. 

The locations of the Keepers are relatively far apart. Because of this it is recommended that you have some means of quick transportation. Arvak will do nicely for this purpose.

Each of the Keepers have 1-4 minions (bonemen, mistmen or wrathmen) that will attack you, usually ahead of your encounter with the Keeper. The Keepers themselves may prove to be quite a challenge to lower level players. One possible strategy for the bow-wielding Keeper is to use Unrelenting Force to blast it off the edge of the tower.

Once the final Keeper is defeated, the quest will update and you will need to return to Valerica. She will then lead you into the Boneyard.  Once inside the Boneyard, you will have to "slay" Durnehviir. There will also be numerous bonemen in combat, but they will die along with him. Let Valerica and Serana handle any of the minions while you focus on Durnehviir. Once he has been defeated, take the Elder Scroll, and speak to Valerica. If you are not a vampire, and allowed Serana to partially soul trap you in order to enter the Soul Cairn, Valerica will instruct you on how to retrieve your soul from a Soul Essence Gem located at an offering altar not far away. The miscellaneous objective "Retrieve the Soul Essence Gem" will lead you to it.

Once you leave the Boneyard, Durnehviir will rematerialize and speak to you, starting his quest. If you tell him you have more pressing matters to attend to, his quest will not begin and you will need to return to him at a later time to initiate it. Afterwards, you may proceed to the offering altar to retrieve your soul if necessary, then travel back to the portal and complete the quest.

Achievements
One achievement is unlocked when you complete this quest:
 

Notes
The soul essence gem can be retrieved before talking to Valerica. If you do so, she won't talk about it.
It is possible to kill the Keepers before talking to Valerica the first time which unlocks a new line of dialogue from her about it. In order to find the Keepers it is a good idea to look at the top of the buildings until you spot ones with debris swirling around the top of them; the only other building that has this look is Valerica's prison.
If you sided with the Volkihar, but cured yourself of vampirism before entering the Soul Cairn, Valerica will still refer to you as a vampire.

Bugs
 
 
 
 
 Enter the Boneyard and defeat Durnehviir, press the "~" key to open console, and type   then press enter. You should be able to fly and move through objects; go to the Elder Scroll case and enter the container to pick up the scroll. This will trigger the next stage of the quest, and solve the bug without creating the later bug in the quest Unseen Visions.
 Another way of solving this is to go into Boneyard and type   first and then   . This will teleport Valerica next to you, and she will resume to her correct pathing. As for Serana, just repeat the process but type   instead.
 
 
To get Serana back, simply go back through the portal to Volkihar. She should appear with you again, and you can then return to the Soul Cairn.
 The console commands   and   will teleport Serana to you.

Quest Stages