Eris Morn traverses a cavern beneath the Moon's surface. She finds what appears to be an artificial surface among the rocks and touches it. The cavern begins to rumble and part of the wall breaks away, letting in light to the cavern. As Eris turns away from the light, a strange Phantom appears before her.
The Guardian travels to the Moon in response to an alert from Commander Zavala.
Zavala: Attention, all Guardians: last night, we detected a seismic disturbance on the Moon. Within hours, it was swarming with Hive. This plague must not be allowed to spread.
Lunar Battlegrounds, The Moon
The Guardian arrives on the Moon, alongside several other Guardian jumpships and Vanguard transports.
Zavala: The Hive pour onto the surface of our Moon from the Keep. That is where our disturbance originated. We will investigate, but first we must regain a lunar foothold. For some of you, this is all too familiar. But do not let the atrocities of Crota haunt you. Whatever this is, we will not let the tragedies of our past repeat themselves.
The Guardian defeats the Hive together with other Guardians and several Redjack Frames.
Ghost: The Hive appear to be retreating. Commander, these Hive are erratic. Scattered.
Zavala: They lack leadership. Crota's death left a void they have yet to fill. But the disturbance seems to have emboldened them. They must be stopped.
Ghost: We're on it.
The Guardian heads towards the next area, where they find Eye of the Swarm, a huge Shrieker, as well as a portal and six Annihilator Totems.
Ghost: Hive are coming from that portal ahead. Let's shut it down.
Gothrax, Protector of the Swarm appears. The Guardian defeats Gothrax, Protector of the Swarm. The Guardian drains the six Hive vigils under the Annihilator Totems.
Ghost: The Shrieker's vulnerable. Now's our chance.
The Guardian defeats the Eye of the Swarm.
Ghost: The portal is down, Commander.
Zavala: Good work, Guardians. Thanks to you, we'll have an LZ up and running soon. In the meantime, press on towards the Keep.
Ikora: Guardian. There's no time to lose.
Ikora: This "disturbance" — I know what triggered it. Who triggered it. Eris Morn.
Ghost: Eris is back on the Moon?
Ghost: Eris? She disappeared before the Red War. She's here?
Ikora: Last I heard from her, she was headed into the Keep. I don't even know if she's still —
Ghost: We'll find her. Alive.
Sorrow's Harbor, The Moon
Zavala: Before we can gain access to the Keep, you'll need to clear the surrounding area. Assistance is on its way.
Ghost: Commander, was the Vanguard aware of the Hive's activity on the Moon before the disturbance?
Zavala: We've been closely monitoring their progress, but had not yet discovered the purpose of this Scarlet Keep.
Another Eye of the Swam Shrieker appears. Vanguard transports deploy three Drake Tanks. The Guardian uses a Drake Tank to defeat the Eye of the Swarm and the Hive.
Ghost: The path is clear. Ready to head into the Scarlet Keep.
The Guardian heads towards the Scarlet Keep.
Ikora: Eris came to me. She'd found evidence of something very old on the Moon. A potential threat to humanity. Eris insisted on going alone. Just a scouting mission, she said. And I let her. Eris is resilient. She's proven that again and again. Often to her own detriment.
Ghost: If anybody can take care of themselves, it's Eris Morn. [static] Ikora? We've lost her signal. That's strange.
Enduring Abyss, The Moon
The Guardian heads further into the cavern and sees a Phantom. The Phantom disappears.
Ghost: What was that?
The Guardian heads further into the cavern, defeating the Hive Thralls which they encounter, as well as two Nightmare Thralls.
Ghost: These Hive… they're not actually Hive. Their energy signature is entirely unfamiliar.
The Guardian heads further into the cavern, defeating the Hive Thralls which they encounter. The Guardian finds a way out of the cavern and sees several Phantoms hovering in the distance.
Ghost: The source of our… disturbance… should be right around here.
The Guardian heads towards the source of the disturbance and finds a Pyramid.
If the player has not done the Invitations of the Nine
Ghost: What… is that? I've never seen anything like it. This must be what Eris was after.
If the player has done the Invitations of the Nine
Ghost: That's… one of those Pyramids. It can't be. That should not be here. Eris must have gone inside.
The Guardian heads towards the Pyramid.
Ghost: Something's wrong. I feel strange. Like someone — or something — is invading my Light.
The Guardian enters an area closer to the Pyramid and sees a strange red orb in the distance.
Ghost: That… thing across the way. What is that?
The Guardian approaches the red orb.
Ghost: There's some sort of massive energy spike here. It's too heavy for us to pass through.
Nightmare of Crota, Son of Oryx, appears.
Ghost: Crota?! But we killed him!
Ghost: Crota?! But he's dead!
The Guardian fights against the Nightmare of Crota, Son of Oryx. After damaging the Nightmare of Crota, the Nightmare of Crota shields itself and heals the damage it has taken. The Guardian receives an unknown essence from the Nightmare of Crota.
Ghost: He's regenerating?
Nightmare of Dominus Ghaul and Nightmare of the Fanatic appear next to the Nightmare of Crota.
Ghost: We can't win. We have to go. Now.
Eris Morn: Guardian! Come… with… me! [Incantations]
Eris Morn teleports the Guardian away from the Nightmares. The Guardian exits from a portal and finds Eris Morn, along with a Phantom hovering nearby.
The Guardian: Eris Morn. What is that Pyramid?
Eris Morn: You've heard the stories. Of the Traveler's sacrifice. Of Darkness descending upon humanity. Before us lies a dark remnant of their existence. Was it struck down by the Traveler? Left here on purpose? The truth is ours to discover.
The Guardian: Discover how?
Eris Morn: We find a way inside.
Sanctuary, The Moon
The Guardian speaks to Eris Morn.
Eris Morn: Ghaul… The Fanatic… Crota. Like living nightmares, your past confronts you, Guardian. Old scars reopen around me as well. Phantoms of my friends return with a malice they never truly had. Every one of them, the twisted will of that looming Pyramid. We must not let it distract us from our goal: finding a way inside. Together, we have conquered our enemies. We will do it again.
Eris Morn: Ghaul… The Fanatic… Crota. Like living nightmares, your past confronts you, Guardian. Old scars reopen around me as well. Phantoms of my friends return with a malice they never truly had. Every one of them, the twisted will of that looming Pyramid. We must not let it distract us from our goal: finding a way inside. We're in this together now. Nothing can stop us.