The Deepening Wake
Travel to Sorrow's Harbor on the Moon and investigate the Hive rituals taking place there.
At the Altars of Sorrow, open a Tier III+ chest and defeat Nightmares.
"Luna's fate darkens with every step the Hive take. I can smell their desperation. Crota's daughters… they intend to turn it to destruction." —Eris Morn
Legendary Quest Step