Quest Stages - TG09 (Darkness Returns)

10 Enter the Twilight Sepulcher
With the Skeleton Key of Nocturnal safely in my possession, I'm bound for the Twilight Sepulcher to return it to its resting place.
20 Speak to the Nightingale Sentinel
25 (Optional) Retrieve Nystrom's Journal
30 Follow the Pilgrim's Path
Within the Twilight Sepulcher, I happened upon the spirit of Gallus, the Nightingale murdered by Mercer Frey. He warned me that removing the key from its resting place has corrupted the other resident Nightingale Guardian Spirits, distorting their morality and making them incredibly hostile.
40 Return the Skeleton Key to the Ebonmere
50 Listen to Nocturnal
60 Speak to Karliah
70 Choose Nightingale Role
200 I've returned the Skeleton Key to its proper resting place within the Twilight Sepulcher and encountered Nocturnal herself. As a reward for my actions, she allowed me to become a true Nightingale Agent and imbued me with the appropriate ability befitting my station.