"A phantom of my deceased fireteam member Sai Mota haunts me. It is only a trick of the Pyramid."
From the Nightmare of Crota, you received an unknown object that harbors a dark energy. You leave it with Eris Morn so she can unearth its secrets.
In the meantime, the Moon hosts further mysteries to uncover regarding entering the Pyramid. The Hive seem to be exhibiting strange behavior that may be related.
Investigate the strange Hive behavior near the Scarlet Keep.