Prophet (Vampire)

Background
Upon returning to Castle Volkihar, Harkon informs the Dragonborn of a prophecy hidden in the Elder Scrolls that, if fulfilled, would end the tyranny of the sun over vampires. He then asks the members of the court to gather in the dining hall to as he makes a proclamation to the court. He orders everyone to locate a Moth Priest in order to read the Elder Scroll.

Harkon's speech
''"Scions of the night! Hear my words! The prophesied time is at last upon us. Soon we will claim dominion over the sun itself, and forge a new realm of eternal darkness. Now that I have reclaimed one of my Elder Scrolls, we must find a moth priest to read it.

I have spread false rumors about the discovery of an Elder Scroll in Skyrim to lure a Moth Priest here. Now it is time to see if those efforts have borne fruit. Go forth, and search the land for rumors of a Moth Priest within our borders.

Look to the cities. Speak to innkeeprs, carriage drivers, anyone who would meet a traveler. Go now, and carry out this task. This is my command!"''

Ask a Carriage Driver
Ask any carriage driver outside a city if he has seen a Moth Priest. He will mention that he's not sure, but can be persuaded or bribed for answers. The driver will reveal that the Moth Priest asked him to take him to Dragon Bridge.

Ask an Innkeeper
Ask any innkeeper in any city if they have seen a Moth Priest. They will reveal that the Moth Priest had recently stayed in the inn, on his way to the Dragon Bridge.

Visit the College of Winterhold
Head to the College of Winterhold, and speak to Urag gro-Shub in the The Arcanaeum. He will reveal that a Moth Priest came by to study in the library, but left for Dragon Bridge.

Dragon Bridge
Upon reaching Dragon Bridge, ask the guards or Clinton Lylvieve about the Moth Priest's whereabouts. They will mention that he left south across the bridge a short while ago.

Travel south across the bridge and eventually an ambushed carriage can be found. Search the vampire corpse for a note indicating that the Moth Priest was kidnapped by a rival vampire faction and taken to Forebears' Holdout.

Forebears' Holdout
Upon entering the cave it seems as though the Dawnguard arrived first and killed the rival vampire faction in order to secure the Moth Priest. Head left and kill the Huskies, Armored Troll and Dawnguard patrolmen before crossing over to the main building and up the stairs to the upper platform. The Moth Priest, Dexion Evicus, is being held here within a magical barrier.

Guarding the barrier will be Vanik, leader of the search party. Once all the Dawnguard are dead, search the corpse of the Orc vampire Malkus to find a Weystone Focus. Place the Weystone on the altar above the barrier to deactivate it. Dexion Evicus will awaken, but will become hostile as he is still under the spell of Malkus. After beating him into submission, use the Vampire's Seduction power to calm him, then bite him to turn him into an obedient thrall. Once Dexion has been enthralled, command him to go to Castle Volkihar.

Travel back to Castle Volkihar and report to Harkon. Next order Dexion to read the Elder Scroll. He first sees a vision of Auriel's Bow, then a voice whispers to him about a dread lord of the night who will rise up in a time when dragons return. He then reveals that two other scrolls are needed to learn the secret of the bow's power and complete the prophecy. One scroll contains the ancient secrets of the dragons, the other speaks of the potency of the ancient blood. Once the reading is complete, the quest ends and Chasing Echoes and Seeking Disclosure begins.

Elder Scroll reading
Dexion: ''"I see a vision before me, an image of a great bow. I know this weapon! It is Auriel's Bow! Now a voice whispers, saying "Among the night's children, a dread lord will rise". In an age of strife, when dragons return to the realm of men, darkness will mingle with light and the night and day will be as one.

The voice fades and the words begin to shimmer and distort. But wait, there is more here. The secret of the bow's power is written elsewhere. I think there is more to the prophecy, recorded in other scrolls. Yes, I see them now... One contains the ancient secrets of the dragons, and the other speaks of the potency of ancient blood.

My vision darkens, and I see no more. To know the complete prophecy, we must have the other two scrolls.''"

Bugs

 * The Weystone Focus might not be found on Malkus's corpse, or the bodies of any other NPCs. There is currently no solution besides the use of console commands.
 * When you go to save the Moth Priest, he may be outside of the magic barrier. If he is, then do not deactivate the magic barrier. If you do, he will stay down after being defeated. Every time you enter Fort Dawnguard or Castle Volkihar, he will attack everyone. The only workaround at this time is loading a previous save.
 * It is possible that Malkar can be in the forcefield making it impossible to open without reloading.
 * Upon releasing the Moth Priest, he will be hostile. After he has been defeated, if he does not stand up and remains downed on his knees, then he will attack the other NPCs at Fort Dawnguard or Castle Volkihar when you travel there. The only current way to remedy this is to load a previous save. To avoid this bug, don't move after opening the barrier until you get a quest update saying to defeat the Moth Priest.
 * Guards do not run through quest script and cannot be interacted with beyond their usual script.
 * Solution: Bypass the need for speaking to the guards by going south out of Dragon Bridge to find the ambushed caravan.
 * Also, talking to Clinton Lylvieve will advance the quest and mark the ambushed caravan on the map.
 * Isran's and Serana's script don't not activate after following Isran. The only known solution at this time is to reload a previous save.
 * After Harkon tells you to have the Moth Priest read the Elder Scroll use Vampire Seduction on the moth priest, feed, and then talk to him. He should read the elder scroll and although he will become hostile again afterwards you my continue on with the quest. This is the only solution I have found other than reloading to a previous save.
 * The Moth Priest may not respond after feeding on him and will only say his generic dialog thus not allowing advancement of the quest.
 * Possible solution: usage the command : "setstage DLC1VQ03Vampire 70" to skip the "feed& thrall part" after defeating him.

Its Possible When You Back To Fort Dawnguard Or Castle Volkihar The Npc's Become Hostile,I Dont Know The Solution