Nocturnal, also called the Shadow Queen, is the Daedric Prince of night and darkness, and the patron god of thieves. Nocturnal was among the Princes who did not sign the Coldharbour Compact, which bound some Princes from manifesting on Mundus. Alongside her fellow Princes Clavicus Vile and Mephala, together dubbed "The Triad," she is responsible for the events of the Daedric War and is the main antagonist of The Elder Scrolls Online: Clockwork City and The Elder Scrolls Online: Summerset.
Inside "The Throne Aligned" of the Cognitum Centralis, once the Shadow of Sotha Sil is defeated, you will be quickly shrouded by shadows and awaken to Nocturnal's dark energy encroaching around Sotha Sil and the Skeleton Key. Proctor Luciana Pullo and the recently arrived Divayth Fyr will be fending off Nocturnal's powers, and have the following exchange:
Proctor Luciana Pullo: "Fyr? Where did you―? What are you doing?"
Divayth Fyr: "Never mind where I came from! I'm keeping Sil alive, you ungrateful shrew! We can't let the shadow escape!"
Luciana Pullo: "Just hurry! I can't hold the light for long!"
Nocturnal: "Even now, at the end, you bicker. How predictably mortal..."
Divayth Fyr: "She's here! Nocturnal!"
Nocturnal: "Why do you struggle so? Do you not see that it's hopeless? Sleep now... give in to the dark."
Divayth Fyr: "I can't hold it much longer! Get up, comrade! You have to turn the Skeleton Key! Now!"
Luciana Pullo: "I... will not yield! Go, friend― do as Fyr says! Unlock the throne! Free Sotha Sil!"
Upon activating the Skeleton Key, Sotha Sil will awaken and banish Nocturnal using his restored energy. Her shadow magic slowly retreats, returning the Throne Aligned to its normal state, and will leave saying a cryptic message:
Sotha Sil: "You trespass, Ur-dra. The Clockwork City shall bear your wait no longer.
Nocturnal: "You achieve nothing, little godling. The Triad looms upon Summerset's shores. All that is shall be ours!"
Divayth Fyr: "Well done, my friend. Enough theatrics, Luciana. On your feet. Luciana...?"
Sotha Sil: "We should return to the surface. This is no place for mortals."
- Nocturnal was originally intended to be involved in the Thieves Guild DLC, but the questline for it was re-designed and storylines relating Nocturnal were cut out.