In the previous quest, "Ritual of Accession," the Hero chose to ascend to either the throne of Mania or Dementia. Depending on the choice, either Lady Syl or Lord Thadon will barge into the Sacellum during the Ritual and announce his or her defection to Jyggalag.
Note: This walkthrough was written from a character who picked the path of Mania and overthrew Lord Thadon. The quest is nearly identical for those who picked the path of Dementia, except instead of fighting alongside Golden Saints one will be fighting alongside Dark Seducers.
Travel to the Fringe. The giant silver crystals that usually accompany Priests of Order have grown all over and the Hero will find a group of Golden saints/Dark Seducers battling a group of Knights of Order. After a brief fight Aurig Desha, one of the Saints, will approach them and say that the Knights are "relentless" and appear as fast as the Saints can kill them. She believes that destroying The Spire in Passwall will rob them of their power, and she has an idea. Before she can tell them however, another wave of Knights approach and they are forced to fight.
At this point, there is an option to allow Aurig to command the troops or taking charge themselves. If chosen to command the troops, they must approach each Saint and order him to flank with a sword, move to the back with a bow, or stand their ground with an axe. Distribute the troops over the field, emphasizing those areas they are weak in. If a marksman, send more in with an axe. If fighting with a sword or touch magic, order more Saints to snipe with a bow. If they tell Aurig to command the troops herself, she will set up a line of ax-wielding front line troops and at least one archer.
Once the battlefield is prepped, notify Aurig. Seconds later, three waves of three Knights will materialize in front of the Spire.
After defeating the Knights speak to Aurig. She will tell the Hero that her scouts have noticed increased activity around the ruins of Xeddefen, located in the southeast corner of the Fringe. As they make their way to Xeddefen, they may notice that the Fringe has become barren, and the giant silver crystals will grow rapidly in their path.
Xeddefen is a fairly large ruin. Look for buttons in walls, traps, and watch the map for the beginnings of hallways behind secret doors. Proceed to the Great Chamber where they will discover Shelden, the self-appointed mayor of Passwall, sneaking through the halls. He says that he escaped into the ruins after the Knights attacked and has been lost ever since. He asks them to protect him. If they agree, he will become a standard follower.
Note: If they do not take Sheldon as a follower he will subsequently be crushed by the collapse of the ruin.
In the center of the next room is a large cluster of Knights of Order and a giant silver crystal with rivulets of light flowing down. One must place three Hearts of Order into the obelisk to overload it. At least one knight will appear after each Heart.
Immediately after overloading the obelisk, the ceiling will begin to collapse. Run north first, then back around to the southwest. Mayor Shelden is apparently incapable of jumping, and if a large section of the ceiling collapses in his way, he will be stuck. However, by just running at the rubble one can carve a path for him by pushing the rocks out of the way. Shelden is also essential, and if he gets crushed wait for a few seconds and he will stand up and follow again.
Follow the red arrow to Felles, a mixture of ruins and caves. The ceiling will not collapse in the root-like cave section, but will continue to fall in the ruins sections. Knights and Priests are scattered throughout Felles. At the final part of the level they will find a door that blocks the passageway west to the exit. The switch is on a pedestal in a room to the south.
As soon as they get through that gate it slams shut, locking Shelden behind. He scolds them and says he will find another way out. The next section - all the way to the exit - is best done at an all-out sprint whilst on skooma, as this greatly increases speed.
Shelden will be waiting outside. He rewards them with absolutely nothing so find Aurig and speak to her instead. She will be in Passwall, fighting off a final wave of Knights. She sends you back to Sheogorath. Note that you cannot fast-travel from the Fringe at this point - you will have to get through the Gates of Madness first.
Once back at Sheogorath's Palace, he will say that their next task will be to restore the Gatekeeper, who they killed in the quest "Through the Fringe of Madness." Restoring the Gatekeeper will keep the rest of the Shivering Isles safer from another invasion.
This will end the current quest and begin the next: "Rebuilding the Gatekeeper."
I've arrived in the Fringe to find that it has been completely conquered by the forces of Order. Passwall may have been attacked. I should take a closer look.
The force of Knights attacking Passwall have been eliminated. I should speak to Aurig Desha about the situation.
I've discovered the source of Order's power -- an obelisk is having its power amplified by the spire that leads to the center of Passwall. I must find a way to shut down the obelisk.
I've survived the collapsing ruins of Xeddefen. I should seek out Aurig Desha and ask her how the battle above ground went.
Passwall has been liberated and the forces of Order have been defeated. I should speak with Sheogorath.