Online:The Ravenwatch Inquiry

Quick Walkthrough
#Find Gwendis at her camp in  .
#Travel to Bangkorai to speak with Scholar Laurette Diel at the Bangkorai Garrison.
#Find the missing scholars in nearby locations.
#Search for the Pyre Watch warrior in the Crypt of the Exiles and talk to them.
#Return to Gwendis and talk to her.
#Go to Viridian Watch and find the Gray Host sanctuary.
#Search the hideout for clues and talk to Gwendis.
#Travel to Ravenwatch Castle and sneak inside with your companion.
#Search the castle cellar for clues.
#Investigate the hidden room and show Gwendis your findings.
#Meet with Gwendis outside in the courtyard and get in the cart.

Detailed Walkthrough 
A Request from the Ravenwatch
There are three ways to begin the quest. Firstly, you can go to the Crown Store and pick up the Prologue Quest: The Ravenwatch Enquiry from the Quest Starters tab. Secondly, you can find and read the House Ravenwatch Contract in the Mages Guild Hall of your alliance's starter city;  . The last way is to come across the Ravenwatch agent yourself, who can be found at her small camp near the aforementioned cities depending on your alliance. Either way it is started, you will need to find and speak with Gwendis outside the city in question. 

She will recognize you if you have met before, and will explain her current assignment. Gwendis is looking into the past of the Gray Host, an army of vampires and werewolves lead by King Styriche of Verkarth, which was on the warpath in the First Era before their defeat in Bangkorai. Recently, a surviving member of the Host's ruling council has begun rebuilding the army and has been experimenting with life energy to devastating effect. In particular, she wants factual information about their defeat at Bangkorai Pass as the she feels the known story of Saint Pelin's miracle is "Outlandish". To this effect, Gwendis wants to talk with the scholar Laurette Diel, who is said to be an expert on the many battles involving Bangkorai Garrison and can be found there. Once you have finishing asking questions, you can fast-travel to Bangkorai via the nearby horse and cart.

To Bangkorai Garrison
You will arrive just outside the gates of the garrison. Looking around, the scars of recent battle are still evident as Gwendis notes. It should be noted that the situation will be the same whether or not you previously reclaimed Bangkorai Garrison for the Daggerfall Covenant from the Seventh Legion.
:Gwendis: ''"Well this isn't at all what I expected. What happened here?"''
Find the Scholars|thumb|right
To the north of your starting location there is a small camp, where you can find Scholar Laurette Diel with her face in her hands. She isn't in the mood to be asked about the Gray Host as she recently escaped the Imperial forces' attack on the garrison. Laurette and her fellow scholars barely escaped with a warrior from the Pyre Watch but they got separated in the confusion. She asks you find her missing friends and suggests the Pyre Watch warrior would be able to help with your inquiries as their Order guards the burial site of the Gray Host. After agreeing to help, Laurette will mention the directions her friends ran in and on further questioning admits she specializes in Second Era lore as opposed to First Era.

Speaking with Gwendis about this, she suggests that you split up to search for the scholars. She'll go to Kerbol's Hollow while you go in the direction of Evermore. The two scholars can be found closer by than the city. Scholar Indouz reached the camp at Martyr's Crossing while Scholar Cogline can be found hiding behind a pillar in Pelin Graveyard. You can direct both of them to Laurette Diel's camp and ask them about the Gray Host. Unfortunately neither of them know much but mention the Pyre Watch warrior headed in the direction of the nearby Crypt of the Exiles.
The Pyre Watch Warrior|thumb|left
The crypt is a Delve to south of the graveyard and north of the Bangkorai Pass Wayshrine. The Pyre Watch warrior can be found in the northern corridor of the ruin near the crates though you can completely avoid the Boss' chamber while searching for her or escorting her out. When you approach, she will be prepared for battle.
:Shelaria: "Come forward, you godless mongrel!"

You may have previously met Shelaria in the Unhallowed Grave and helped her stop the Draugrkin plunderers. Nonetheless, you can explain what you are doing there and assure her the scholars are safe. You can then lead her outside where she will thank you for the assistance and asks how she can help you in turn. Upon asking about the Gray Host and their defeat she acknowledges that the story is mired in legend but says magic was involved, "[...]but whether it was divine in nature or Alessian sorcery we have never been able to determine." However, she does know there were records of a survivor of the battle who took refuge with a member of the Direnni. Shelaria further recalls a mention of a sanctuary at Viridian Watch which only the worthy could enter.

Return to the Diel's camp and Gwendis will have found Scholar Jeanard. Tell her what you have learnt from Shelaria and Gwendis will agree it corroborates with her prior research. As it is your best lead she'll mark the place on your map and is eager to escape Diel's stories about Saint Pelin. 
The Sanctuary of Viridian Watch
Follow the Sigils|thumb|right|"Only those worthy can find the way to safety"
Viridian Watch is another delve to the northeast, which is home to the Bjoulsae Boys bandits. Once you enter Viridian Watch, Gwendis will enter behind you and quickly notices something:

:Gwendis: "Look!"
: 
:Gwendis: ''"There's a sigil! Right there! Don't you see it?"''

If you are a vampire or a werewolf, you will see be seeing the same thing as Gwendis, a glowing red sigil on the floor. Otherwise, you will just see Gwendis pointing at the ground. Speaking with Gwendis, she'll make it clear, "Only those worthy can find the way to safety … only vampires and werewolves can see these sigils! That explains why no one ever found anything." In the case you can't see the sigil, Gwendis will have a solution. She hands you the   containing some of her essence, which allows you to see the sigils. As you follow the path of sigils while fighting off Bjoulsae Boys, Gwendis will keep track of where to go next. The path leads to a small room behind the spawn point of the delve's boss, Curnard the Generous. Gwendis will walk over to the blank wall and exclaim:
:Gwendis: "Ha! This must be it! Now, how to go about opening it?"
She pokes at the brickwork and a red swirl of light soon appears which turns into a glowing pattern on the wall.
:Gwendis: ''"That's done it! Let's check inside!"

Following her in, you will find a small room which has been undisturbed for a long time. On a crate, you can find the Letter of Welcome'' which is addressed to Rada al-Saran from the Direnni clan member. You may recognize Rada al-Saran as the man behind the current reemergence of the Gray Host. Gwendis also recognizes the letter's author from a previous adventure:
:Gwendis: "Rada al-Saran was the survivor! That figures. And Lady Thorn helped him. Or should I say Lady Ingerien?"

But there are still many bags and boxes to search through for clues, Gwendis will lightly remark on the   and   but becomes very concerned when you find the  :
:Gwendis: ''"Wait, what's that? Let me see it."''
Gwendis recognizes the signet ring as near identical to one she last saw in the possession of her own mentor, Count Verandis Ravenwatch himself, of western Rivenspire. It implies a connection between him and the Gray Host which disturbs Gwendis, who will want to look for answers closer to home at Ravenwatch Castle. You will be offered the opportunity to fast-travel there or you can make your way there on your own.

Investigating Verandis
If you completed the Rivenspire Zone storyline beforehand then you will have previously met Count Verandis Ravenwatch. Your last meeting with Verandis was when he sacrificed himself to prevent the Lightless Remnant from unleashing its curse on everyone in Rivenspire upon its destruction. In either case, Gwendis will be waiting for you in the courtyard behind the castle. Speaking with her, Gwendis explain that she wants to sneak in to find evidence of Verandis' connection to the Gray Host or evidence to exonerate him. Depending on the status of Verandis her reasons will differ—if Verandis is still alive, she wants the facts before she confronts him. If he is gone, she doesn't want to her family to know and potentially sully his name in their eyes. Even if it happened a long time ago, she wants to know why he has gone to great lengths to hide it from everyone, including her. To that end, Gwendis will want to check the cellar as that is where Verandis stored the various things he collected over the centuries.
Verandis keeps his secrets well hidden|thumb|right
After agreeing to help her investigate the castle cellar, she will walk up to the stables and begin shoveling until a trap door is revealed. You can then enter the secret tunnel and sneak into the castle, it is a short trip but be aware of the giant spiders, skeevers and a small Bone Flayer or two. Once inside the castle, follow Gwendis downstairs until she unlocks the cellar door. The room is filled with crates and boxes and you may need to search through them all.
:Gwendis: "See if you can find the signet. It must be in one of these crates or boxes."

Looking through the various boxes, Gwendis will remark on them but no luck in finding anything. However, the armoire is much more interesting:
:Gwendis: ''"Another secret door? I didn't know that was here. It has the same mark as the signet. Maybe …."
: 
:Gwendis: "It opened! Let's see what's inside."''
What's in the abandoned study?|thumb|right
The small room on the other side is dark and the furnishings are covered in dust and spiderwebs.
:Gwendis: "What is this place? Did Verandis use this as a secret study? Check the desk, would you?"

Read the letter addressed to Verandis as My Dear Friend, it is from Rada al-Saran where he requests that Verandis take a break from [His] quest to appease and coddle the mortals and come visit Grayhome. A castle recently constructed on a secret island as a home for the Gray Host. It also refers to the Host's ruling body as the "Gray Council" and that Verandis' absence from their table is felt. He also mentions to the Exarchs Ulfra and Tzinghalis who may have been previously encountered in Western Skyrim. With a final plea for Verandis to return home to his family the letter ends.

Show the letter to Gwendis who will be hoping the letter isn't what she thinks it is. Upon the apparent proof that Verandis was part of the Gray Host—and the ruling council at that—Gwendis will insist that there must be more to it. At the mention of Grayhome castle, she will want to investigate if there is a chance it still exists in the search of answers. She'll will first want a moment to look around before meeting you outside. She will be waiting for you in the courtyard near the cart where you can talk with her once more to complete the quest.
:''"I think I'm as ready as I'll ever be. Delaying the inevitable won't help anyone. And it won't get me the answers I need. Come on, let's go see what's on this secret island."
:What do you think we'll find on this secret island?
:"Answers, I hope. Look, I have to do this. I'm going to see this journey through, no matter what truth waits at the end. Let's just go. The sooner we get this over with, the better. First, however, take this. You earned it."''

You will receive some gold and can continue to speaking with Gwendis to start your journey to Grayhome.
 

Bugs
 
This issue can be fixed by abandoning this quest.
 

Quest Stages