The Guardian joins Osiris on the Moon in his hunt for vengeance.

Zavala: Guardian, we have a developing situation that I need you to take point on. For the past few weeks, Osiris has been trying to assess the damage caused by the return of the Darkness. He believes that Xivu Arath, the Hive god of war, seeks to take advantage of the power vacuum left in its wake. Osiris was investigating physical manifestations of her magic near the Scarlet Keep when… his Ghost, Sagira, was slain. Osiris delivered a message through a secure channel requesting that you personally aid him in this hunt. He's desperate, Guardian. I need you to save him from himself.

Archer's Line, Ocean of Storms, The Moon

Ghost: I'm… I'm worried about Osiris. If Sagira's gone, then —

Osiris: Don't worry about me, but keep your voice down. I'm using an external comm. I thought I was hunting Sagira's killer… the High Celebrant of Xivu Arath. But now I think it's hunting me. Meet me in the Hall of Wisdom.

Ghost: He cut the transmission. We have to hurry.

The Guardian proceeds into the lunar caverns.

Glint: Your friend is in a lot of danger.

Ghost: Who are you?

Glint: A concerned Ghost. Osiris shouldn't be here, especially in his condition.

Ghost: We appreciate the warning, but we know what we're doing. If you and your Guardian are here to help…

Glint: My… Guardian. Right.

Hall of Wisdom, Ocean of Storms, The Moon

The Guardian explores the Hall of Wisdom.

Ghost: Osiris? Can you hear us?

Osiris: Yes, I can hear you! I'm luring the High Celebrant to the Shrine of Oryx! They're — damn! It erected a barrier. I think it knows you're here. It's trying to keep us separated!

The Guardian defeats the nearby Hive removing the Hive barrier. The High Celebrant appears.

Ghost: That Knight is radiating strange energy… It has to be the High Celebrant — the one that killed Sagira! Osiris, we're here! We'll get that barrier down!

Osiris: Keep your Ghost close, Guardian.

The High Celebrant retreats. The Guardian witnesses a Hive cryptolith. The Guardian removes the Hive barrier and gains access to the Shrine of Oryx.

Ghost: Osiris, it's heading your way!

Osiris: Good.

The Guardian pursues the High Celebrant.

Osiris: I've retreated deeper into the shrine. I think this may have been a trap… That tower you saw on the way in, that's a Hive cryptolith. It's a conduit of Darkness. One of many. The High Celebrant is using them to deploy soldiers across dimensions and… and tempt others to Xivu Arath's side. If I don't make it out of this, I want you to tell Saint —

Ghost: Tell him yourself.

Shrine of Oryx, Ocean of Storms, The Moon

The Guardian find the High Celebrant within the Shrine of Oryx and it retreats summoning more Hive. The Guardian defeats the Hive.

Glint: Guardian! Picking up multiple Hive signatures headed Osiris's way! We're closing in but facing heavy resistance!

The High Celebrant disappears and an ascendant portal appears. The Guardian enters the ascendant portal and is ambushed by the High Celebrant's Hive.

Ghost: We have to get out of here!

The Guardian exits through another ascendant portal and returns to the Shrine of Oryx regrouping with Osiris.

Osiris: You're here! Finally. Is it done? I'll come down to y — Oh!

A Hive Knight appears behind Osiris and knocks him down.

Ghost: Osiris!

The Hive Knight raises its sword to strike Osiris, but is stabbed and killed from behind. The Awoken glares at Osiris and a Ghost appears.

Glint: We warned you it was going to be dangerous down here. Especially for the Ghostless. I'm… I'm glad to see we're all okay, though. I'm Glint, by the way. It's a pleasure to meet you all.

Osiris gestures a wave.

Glint: Go on, introduce yourself.

The Crow: They call me… the Crow. My boss wants to see you.

The Guardian blankly stares at Crow.

Ghost: Impossible.