High level Temple Quest from Almas Thirr.
The player is told to report to an Ordinator outside a small-ish town in the Sacred Lands (choose one that needs some quest love). The Ordinator (who wears no helm) explains to the character that they are hunting a Daedra only known as the Face Stealer, that has been stealing souls and using them in various profane rituals and enchantments. The Ordinator asks the player to escort them to the creature's lair and help kill it.
The lair is half Daedric ruin, half cave, with various ritual implements scattered around. It should also be filled with cultists, dead and alive, who have the bodies of one race but the heads of another (See this asset request: http://tamriel-rebuilt.org/asset/faceless-ordinator-and-other-beasties). They finally come to the last room that is locked. The Ordinator explains to the player that they managed to seal the Face Stealer into this room, which has no lights. Since the Face Stealer will not be able to see the player, their power will be severely limited. The Ordinator tells the player he/she must kill them in the darkness to prevent them from stealing their face.
The room on the other side of the door should be completely dark, and preferrably resistant to such spells as Night-Eye and Light. Someone in there forcegreets the player a few steps in: "Wait! Hold your weapons! I am (Ordinator name), the real (Ordinator name) as ordained by Almalexia herself! That man out there...he is the true Face Stealer! Surely he believed you would strike me down before the truth would be revealed in this thrice-cursed darkness..." (or something similar)
This Ordinator is faceless, and explains how the Face Stealer had tricked him by masquerading as one of the villagers, much like how the Face Stealer tricked the player. He has a plan, though desparate, telling the player to take his Ordinator mask and wear it while fighting the Face Stealer, saying that being confronted with Nerevar's holy visage may confuse the Daedra long enough to kill it.
The player leaves the room. The Face Stealer will attack on sight. If the player wears the helm, the Face Stealer also gains a Ordinator-like head and is severely weakened. The Daedra may also say something referencing that this works partly because the player is Nerevar's Incarnate, so it's not just the mask hurting it. If the player doesn't wear the helm, the Face Stealer casts powerful Drain and 100% Blind spells on the player. (It is okay, even intended, if this means the player dies).
Once the Face Stealer is dead, the player can return to the dark room to tell the Ordinator the deed is done. The Ordinator thanks the player, but asks if they could have their helmet back to hide their own terrible visage. He only hopes a Temple priest can restore his face to normal. Once he gets his helmet, the Ordinator asks the player to escort them to the nearest Temple, being as they are also blinded and cannot see the way themselves. At the Temple the player is given a 500 gold reward and a magical item for a reward.