This is not a quest, but a voice-acted scene at the end of Seeking Their Counsel.
The player meets Alvu and Simine in Necrom's basement. Eagerly, they being the ritual to summon Alandro Sul through the four ringlets. However, they are interrupted by Verendas Hlervan, who says they are committing a terrible heresy, and it is his duty to put a stop to it. Somewhere in here it should also be discovered that the Nerevar bonewalker has mysteriously disappeared from the room as well.
Verendas's perspective: Verendas serves as a counterpoint to Simine's doubt and Alvu's willingness to throw heretics under the bus, in that he has remained resolute to his faith and loyalty to his people. Whereas Alvu and Simine want answers (if for different reasons), Verendas would confront them with the idea that they are better off not knowing, that it is more practical to wait and watch instead of adding more fuel to the fire with new knowledge. He warns them this could start a religious civil war that would muddy the truth and hurt both sides.
The player could:
1) Pick a fight with Verendas, saying they WANT the Temple to break up.
2) Reason with him, obtaining his permission to go through with the ritual. He may or may not stay behind to witness the ritual, depending on how the player convinces him.
3) Refuse to stop, in which case Verendes would attack to stop the war he foresees
4) Agree with Verendes, and stop the ritual. This would end the quest, the NPCs stay where they are making frowny faces at each other. Later, rumors indicate Alvu dying from her old age/poor health. Her mace is left behind in the ritual chamber however, suggesting her dissappearance might not have been from natural causes. Nearby is a pile of dust, which might be Alvu, or might be Nerevar's bonewalker, which has also disappeared. Simine reappears in Holamayan, no longer a member of the Temple and with a broken faith, who does not say much to the player about what happened. Verendes acknowledges they "investigated the matter", but is tight-lipped about the outcome, or what happened to Simine or Alvu. He has been going blind--which may have to do with seeing the mural, or may be due to getting old, it is not clear.
Otherwise, after Verendas is dealt with (possibly through combat, possibly through dialogue), the ritual to summon Alandro Sul is finished. Each ringlet speaks with fragments of Alandro Sul’s voice, giving clues to the location of a holy relic that will answer the priestess's questions and how to get to it. As each ringlet is understood to be an influence of the House of Troubles, each clue should reference the Bad Daedra as testers and teachers of the Dunmer faith.