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||Starting Location: Arcane University
|Starting NPC: Tar-Meena
|Possible Reward(s): Mysterium Xarxes
The starting location for the quest is not actually Tar-Meena, but rather after you find the hidden message on the crypt in the cemetery on the Palace grounds, from the Path of Dawn quest. At noon, the precise location of the Dagon Shrine is displayed, and your map updated. If you look to your map, you'll see it labeled as Lake Arrius Caverns in the northeast section of the map. One word of warning, this is not an easy quest once inside, so get prepared either for battle (health potions, repaired, etc.) or to run though a small dungeon full of enemies (which is viable). If you fight, you'll be fighting lots of Mythic Dawn agents who often summon their own Daedric armor and/or zap you with magic. Nevertheless, it too is roughly scaled to your level and if you've done your share with combat (and you should have by this point) or running, this will not be much different.
Enter the Lake Arrius caverns, just north of the lake, and head down until you see the Mythic Dawn doorkeeper. Don't attack just yet, but give the countersign and then head through the door until you shortly meet Harrow. This is where you'll want to make a decision. He's going to ask for all your belongings, including gold, which he'll personally carry the entire time you're here. If, later, you start battle (and inevitably you will), you will have to kill Harrow for them before you find them on his dead body. If you feel like running through the dungeon and then coming back to deal with Harrow later, you're still going to have to defeat several Mythic Dawn to get your stuff back, so my suggestion is to stay and fight, and refuse to give your things.
A side note. For the sake of completion, let's say you give your belongings to Harrow, don the Mythic Dawn regalia and enter the Shrine Antechamber then the Dagon Shrine where Camoran is giving his speech. Everyone is friendly toward you, and after the speech you approach the dais, where his daughter Ruma commands you to kill the prisoner to show your devotion. If you take the nearby silver dagger (next to the Mysterium Xarxes book), and kill the slave, several Mythic Dawn will leave the room, making the upcoming battle slightly easier (unless you're running anyway). If you, however, refuse to kill the prisoner, everyone attacks, and you have a room full of angry Mythic Dawn. A couple will follow you out if you decide to make a run for it. Yet all your gear remains on Harrow.
Let's assume you're going to fight. You'll have to fight your way to the Dagon Shrine, and that means after Harrow and the doorkeeper are defeated, head through the next door to the Shrine Antechamber. Dispose of any resistance there in the narrow hallways, take note of the first door on your right, and explore if you feel up to it. When ready, come back to that door, which leads to the Dagon Shrine, and interrupt the party below. There are several Mythic Dawn here, so best equip an Area Effect spell if you have one, as well as powerful potions. However, alternatively you can simply run them around, steal the Mysterium Xarxes book on the top of the stone table on the dais in the center of the room, and head back up the stairs and to the right out the north exit. Note that the other way will seal off once they are alerted to your presence in the Shrine.
The north exit brings you to the Living Quarters, a counter clockwise set of corridors and larger rooms, with one central large room at about 9 o'clock. Be sure to search the chests and other containers within the quarters if you're choosing to fight or stealth. A few are Hard and contain more valuable goods. Make your way around to almost the end (about 5 o'clock), where a door back to the Shrine Antechambers is. Skip it and continue on up a slope and then around to another exit to the Lake Arrius Caverns, the same ones you entered by, except in a hidden section. Turn the crank in the next room, revealing the hidden doorway, and then make your way back out.
Now that you have the Mysterium Xarxes, you'll want to take it to Cloud Ruler Temple to Martin. While Martin ponders over its text, he sends you to Jauffre for your next quest, which is to deal with Spies