Skyrim:Restoring Order

Quick Walkthrough
#Discover the location of the conjurer's lair.
#Investigate the Solitude sewers.
#Explore the root cave.
#Defeat Thoron.
#Retrieve the Sword of Jyggalag.

Detailed Walkthrough

While completing the quest Balance of Power, you will learn that the Saints and Seducers are being funded by a conjurer named Thoron. While one journal will mention he is insane and living in the sewers, the other will mention he's located in Solitude. Both journals indicate that Thoron is looking for trinkets and junk, although his motives are a mystery to both bandit leaders. After entering Solitude, the map marker will direct you to a manhole cover leading down into the sewers. 

Straight ahead is a grate, and left is a barred door, so turn right and head down. Across the water you'll see that the tunnel is overgrown with strange-looking plant life. Enter this "root cave" and you'll notice pods that you can harvest for new types of flora. To the right is a dead end with a hollowed stump filled with random loot. Turning left will lead you into a tunnel system populated by Elytra and Spriggans. Further into the tunnel you'll reach an intersection. The right path leads to a small cave chamber populated by Spriggans, along with a dead end containing a dead hunter and goat. 

Continuing along the root path, you'll see a chamber ahead where some of the Solitude stonework is visible. Kill the Elytra Nymphs in the chamber, and to the left you'll see a chamber with water. From the water, you can either turn right to head up a ramp into further root tunnels, or you can go through a broken sewer wall to re-enter the sewers. If you follow the sewer path, you'll come to a room with a Spriggan and some elytra, as well as a locked chest (in an alcove behind the debris).

Following the root tunnel will take you up and around, coming to an intersection where a fight apparently took place. Scattered around the intersection, you'll find both Golden and Dark armor/weapons... but no bodies. There is a short path to the right, but it's just a dead end with some enemies and a hollow stump. Continuing straight from the battle site, you'll come upon the object of your quest - Thoron, the mysterious benefactor of the Saints & Seducers gangs. The obviously insane conjurer appears to be performing a ritual, opening a doorway of some sort.

Once you're close enough, the objective will update - you must defeat Thoron and stop his ritual. Thoron can be a handful - he will summon both Golden Saints & Dark Seducers, in addition to the usual atronachs. Once you've finished him off, make sure to loot his body for a unique Madness Helm as well as several spell tomes teaching you how to summon Saints or Seducers.

From the 4-way intersection where you encountered Thoron, only the southern path leads anywhere (back to the beginning sewers). The northern alcove is Thoron's workstation, where you can find an arcane enchanter and numerous other items of interest. Make sure to loot it all, as both the note and the Sheogorath-Shaped Amber are needed for other quests. The notes begin the Amber and Madness Smithing quest, while the Sheogorath-Shaped Amber is needed for Staada's Quest. 

In the western alcove, grab the Sword of Jyggalag from the roots in order to complete the quest.

Notes

After completing the questline, a courier may track you down and give you a note. It's from Ri'saad, letting you know that he now sells Golden/Dark items as well as the new materials added by the creation.

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Quest Stages