Online:Through a Veil Darkly

Quick Walkthrough
# Use the Uncut Gemstone and speak to Vanus Galerion.
# Investigate the Oracle Marieve's campsite and talk to Wyress Aelynn.
# Read the note in the Mines of Khuras and summon Vanus Galerion.
# Use the three elements in the ritual bowls and speak to the Oracle's projection.
# Use the portal in Bewan to enter The Spiral Skein.
# Talk to Oracle Marieve.
# Set the Oracle free by destroying the binding pinions and fulcrum.
# Talk to the Oracle and travel to Skywatch.
# Talk to Vanus Galerion.

Detailed Walkthrough
Talking to Vanus
After accepting the quest from the Crown Store, a   will appear in your inventory. Activating this will summon a projection of Vanus Galerion, the Great Mage of the Mages Guild who is in need of your helping following a rather unsettling prophecy that mentions you by name directly.

Head to the Mages Guildhall in your Alliance's starting city where you will discuss the situation with Vanus Galerion in person (you can also accept the quest directly from Vanus there, instead of accepting it from the Crown Store). He tells you that the seer who made the prediction, a one Oracle Marieve, is no longer responding to his projections and he fears that she is in grave danger. He also mentions that she predicted you would be the one to save her too.

Hunting for an Oracle
Vanus points you towards Oracle Marieve's campsite, which can be in one of three locations, depending on your Alliance:  . You can get there by using an enchanted boat that Vanus has kindly given you use of. By the time you arrive at her reclusive retreat the surrounding area has been overrun by hostiles. Fight your way through to the campsite. There's no clues but luckily one of Oracle Marieve's Wyrd sisters, Wyress Aelynn, is there.

She will tell you that there is an old Wyrd site in the Mines of Khuras in Glenumbra where she may be, as it makes for a good hiding place. 

Take the enchanted boat which will plop you right outside the delve entrance. Fight your way through to the well hidden alcove deep in the mines.
In the boss area you will find a small tunnel, with green vegetation on it, you need to take to actually find the oracle. It is on the right side if you face the boss. Very easy to miss!
thumb|right|Marieve's projection contacts you and Vanus Galerion in the Mines of Khuras
Watch out though, there is a Wraith-of-Crows—one of Nocturnal's powerful minions—who will eviscerate an unwary player if they aren't expecting it.  If Wraith-of-crows kills you, a hint on the death summary mentions a light switch on the west wall that will disable Wraith-of-Crows' main attack.

You'll come to a small inlet. Read the Note to Vanus to be able to summon Vanus Galerion to your location. He will muse that it looks like a ritual was hurriedly left for one to perform should they wish to speak to the Oracle.

It's a very uncomplicated ritual to perform as well. Collect a feather, a gourd full of water, and an uncut gemstone and place them in bowls with primitive pictographs etched on the base. There are no repercussions should it be done incorrectly, but here is the solution:
:Leaf bowl – place the feather
:Swirl bowl – place the gourd of water
:Triangle bowl – place the gemstone

This will summon a projection of the Oracle who reveals she has been captured and is currently being taken to the ruins of Bewan in Auridon. You must leave the ruins and once more take the enchanted boat to the ruins of Bewan. Luckily you can use a raised ledge to avoid the Wraith-of-Crows should it have respawned.

Fight your way through or sneak through the Sea Vipers there and head to the library chamber at the southernmost point of the ruin.

R. L. Skein
thumb|right|"Time is short ... the dark princes have almost achieved their goal ... you must help me ..."
As soon as you get to the library, Viscount Lelorion snatches the Oracle and pulls her through the portal to The Spiral Skein, Mephala's web-filled realm. You must follow suit where upon you will end up in the same place. Follow the corridor, fighting the many spiders that Viscount Lelorion unleashes on you as you make your way through the halls. He will taunt you throughout but you will finally make it to the entrance hall and must fight Viscount Lelorion before you can progress. 

After that speak to Oracle Marieve who will explain just why Mephala abducted her and tells you that you need to destroy the binding pinions currently being used by her minions to release her. 

You will need to defeat both Weavers Ulfaduug and Gwaumanus and destroy the pinions they are guarding. They are both Spider Daedra with no special abilities and have quite large areas to fight in, so feel free to move away from the narrow ledge edge to avoid being trapped or falling down.

Once that's done you need only smash the center fulcrum to release the Oracle. She will use residual energy to open a portal back to Skywatch through which you must go.

Back in Skywatch
Once you pop back, all you need to do is talk to Vanus Galerion who thanks you for recovering the Oracle and stopping Mephala's plans. He promises to show Marieve the hospitality of the Mages Guild and will reward you with the   for your efforts.

If you want to speak to Oracle Marieve now is the time to do as she will not be present in the game world after you've left the area.

Notes
As with The Missing Prophecy and Of Knives and Long Shadows, the events of this quest form a prologue quest for future content. In this case, the quest acts as a prologue to the events of the Summerset Chapter.
The title of the quest seems to be a reference to the Bible quote "For now we see through a glass darkly" from the New Testament.  This is also referenced by an Oblivion quest, Through a Nightmare, Darkly; and a Skyrim Creation Club quest, Through a Glass, Darkly.
If you complete the quest without the book being read, a copy can be found in the Bangkorai Garrison in Bangkorai. 
With the release of Summerset, the journal entry: ''"Oracle Marieve thinks she's being taken to an Ayleid ruin in Auridon called Bewan. I should go to Bewan and attempt to rescue her."'' was replaced with a line calling the ruin Aldmeri.

Quest Stages