This page explains how to complete the level 80 post-Shadowbringers quest "Fraying Threads".
This quest is available if you have completed the quest Heroic Dreams.
Starting the Quest
Talk to Ryne in the Crystarium to begin the quest.
Speak with Thancred
Go down the stairs of the tower and go southeast to the Aetheryte Plaza. From the Aetheryte Plaza, go east through the archway, then at the base of the stairs, go north through the archway to enter Spagyrics. Go to the quest icon and talk to Thancred to proceed. There will be a cutscene.
Speak with Tataru at the Rising Stones
You can either teleport to Mor Dhona, or you can go into the Ocular and use the Portal to the Source to return to the Source, and go southwest to the exit to North Silvertear to go to Mor Dhona. Enter the Rising Stones and talk to Tataru to proceed. There will be a cutscene.
Enter Dawn's Respite
Check on the Entrance to Dawn's Respite. There will be a cutscene.
Speak with Krile
Talk to Krile to complete the quest.
Next Main Scenario Quest
After you complete the quest, talk to Tataru to accept the next quest: Food for the Soul.