The Sanctuary, a large facility compound that is still intact, hidden in the middle of large cliffs and rough terrain, covering the place up and making things difficult for ground forces to infiltrate. Corporal Rhodes and his team was force to find some way to get through, forcing them to climb over the cliffs with grappling hooks, shooting them to the top and start grabbing onto the ropes and climb to the top. Doom was to be the last one to climb up, standing guard at the bottom and waiting for them all to start climbing, once it was just him, he turns back and starts climbing up the cliffs.

"I wish we could have bought some transport." One of the Crusaders said while climbing

"Just be careful." Corporal Rhodes said "Were almost to the top."

All the Crusaders made it up to the top safe, getting a large view of the place, seeing the large facility in the middle. Rhodes takes out a modified binoculars and got a look at the facility, zooming in on the scope, seeing the entrances is under the guard of demons, seeing many demon soldiers patrolling the area. Rhodes lowers the binoculars and looks back when seeing Doom coming to the top, he lends his hand out to help him up then give him the binoculars.

"You should check a look at it." Rhodes said, looking back at the facility while Doom stands next to him, looking at the facility "The place is crawling with demons."

"So that's the Sanctuary." One of the Crusaders said

"Why are demons patrolling the place?" Another one asks, turning his head to Rhodes

"I don't know…" Rhodes respond "Maybe there's something in there that is making them stay guard."

"Guess we got no choice now." Said one of the Crusaders, holding onto his assault rifle with both hands

"Well we got this guy." One of them taps the side of Doom's armour with the end of his weapon "I'm sure we can handle this."

"Alright… Let's move guys."

Corporal Rhodes and everyone else moves off the cliff, sliding down the edge of it and moving closer to the ground. They land at halfway, getting a few Crusaders staying where they are, watching the demons while the rest go down, once they go sliding down, the rest of them follow. The demons did not see them so they kept moving around, patrolling the area while the Crusaders move closer, moving close enough to give the signal to attack.

Doom Slayer came out of cover and runs towards them, two demon soldiers turn their bodies towards Doom, before they could shoot, Doom takes them out. He fires his double barrel at one of them, blowing its head off while running to the other one, kicking its chest and sending the soldier to the ground for him to stomp on its face. He looks to the Crusaders while reloading his weapon, signalling them to move out. Corporal Rhodes and the others move out of cover, moving closer towards the door, soon to see demon soldiers coming towards them, making the team to shoot them all dead before breaching the door.

One of the Crusaders takes out a large explosive charger and attaches it onto the front door, there he starts putting a timer on it while everyone else moves away. He put the timer for a few seconds, giving the Crusader time to run back into cover before it explodes. Once the door breaches through, Doom charges right in, charging in with his double barrel, seeing a demon soldier and blew its upper body off while the rest of the Crusaders charge in too. Everyone charges in gun blazing, firing at the demons while they shoot back, seeing many demon soldiers in the room, firing back at them but during the firefight, something strange goes down as someone was broadcasting in the room, shouting out to everyone.

"Stop shooting!" Said some man on the microphone, hearing his voice in the room "Stop shooting, stand down!"

The Crusaders and Doom stopped for a moment, looking at the cameras in the room, seeing the voice came from them. Doom turns his head back to the demons, seeing only three remains out of seven and is shock to see the demons just standing there, lowering their weapons and not attacking. Rhodes and the other Crusaders notice this, they too are shocked to see what is happening but somebody would explain this.

A door on the right corner of this room opens up, getting some Crusaders to take aim and noticing this scientist coming through the door, causing them to lower their weapons. This scientist appears in his mid-forties, having no hair and wears a proper scientist robe over his normal clothes. This man rushes into the room and stood between them and the demons, he was breathing heavily as he must have went running through the corridors to reach here.

"Everybody calm down… Relax." The man said while taking a deep breath then exhales. Once he finally calms down, he turns to the demons behind him "Return to the others."

The demons turn to the right and walks out of the room through the right door. Corporal Rhodes steps in "How is this even possible!?"

The scientist turns towards the Crusaders and Doom "Allow me to explain myself… My name is Doctor Carmack I run this facility. I have been waiting a long time for you people to show up."

"You were waiting for us?" One of the Crusaders said

"Do you have any idea how hard it was for me to stay alive, waiting for the UAC to arrive to get me out of here?"

"We… We're not UAC." Rhodes said

"You're not?"

"Can you please explain to us just what just happen?"

"Oh right… Please follow me and I'll explain." He turns to the side and moves towards the door on the left. He raise his head up at one of the cameras that is above the door, saying "Deploy drones at the entrance."

The Crusaders looks at one another then to Doom, seeing him lowering his weapon and follows Carmack. Rhodes and the others follow Doom, staying by his side while they go through that door, seeing two white robotic cyborgs walking past them, arm with plasma rifles. Doctor Carmack would explain to them while they move down the corridor.

"After the demons pretty much conquered the world, my scientist and I was told by the UAC to create some type of weapon to fight against them. We were using biological weapons against them. There has been some setbacks after many scientists decide to give up and escape, they didn't even make it out of here."

"The demons… How do you control them?" Rhodes asks

"It is science." Carmack said "Me and what is left of my team began studying a new way of facing the demons, through ways that can be done by using their own weapons against them."

The team came into a large rectangular part of the facility, lot of broken computers and many large cylinder shape tubes in the room, all against the wall. Most of them are empty and broken, the rest have large demons inside of them, some are small but those that are big stay in larger tubes. In the room, there are twelve cyborgs in the room, doing their regular duties in the room. Carmack walks to the end of the room while the men watch, getting a look at the place before moving ahead.

"Where's your science team?" One of the Crusaders asks, turning his head towards Carmack

"This is all I have left of my team." Carmack said, looking at the cyborgs in the room

Corporal Rhodes turns to Carmack and walks straight towards him "The demons… How are you controlling them?"

"Good question… How does one, control demons through their mind? Well in science term, nanites. We have been designing new type of weapons against the demons but a good method of defeating your enemy is through their own weapons, using their own demons against them. I have created nanites that can do such a thing, which was very hard to accomplish believe me. There was many setbacks, having demons blown up and sometimes the nanites takes longer to control them but I finally pulled it off."

"How the hell did you even get it in them?" One of them asks

Doctor Carmack walks towards one of the tables nearby, opening up a square briefcase and showing two small orbs with spikes all around it, he takes one out and shows it to them "These things."

Doom takes the orb off Carmack, examining the object before looking back to him. "I put the nanites inside those little grenades, think of them as mind control grenades. All I have to do… Well… All these guys have to do…" He looks at the cyborgs for the moment then back to them "Is throw these grenades at the demons and they get stuck onto their body, the nanites will explode into the body of the demons and then take control of their bodies. The demons will serve as drones, weapons to be used against the demons."

'How come you haven't unleashed them yet?" Rhodes said

"A small group of fifty demons won't work against the thousands of them." Carmack said "I was waiting for the UAC to arrive, that way I can get the hell out of here and get the materials to be used to combat the demons."

"You only have fifty?" One of the Crusaders asks

"Well I lost a few… Thanks to you guys. I can't make any more demons now, I used all of my resources on creating them and now this is all I got."

"So you need transport out of this area so you could continue your research, is that it?" Rhodes said

"Yes. I need your help; I also want to bring my research with me. Can you guys do it?"

Rhodes scratches the back of his head with his left hand then turns to Doom "Do you believe this?"

"Wait a minute…." Doctor Carmack said, moving closer towards the group, making them take a step back except for Doom who stood there looking back at him. Carmack walks closer to him, raising his hands forward, looking at Doom's face through the visor then to the side, seeing the symbol on the side of his helmet "It can't be…"

"What's wrong?" Rhodes asks "You know this guy?"

"You're the Doom Slayer." Carmack said "I have heard about you… You are –"

A sudden alarm went off, ending the conversation right now, causing everyone to look up at the ceiling, noticing the red lights in the corner going off. Doctor Carmack runs past them and checks one of the computer systems, looking at the screen, seeing a few red signatures getting closer to the Sanctuary.

"It's the demons." Carmack said

"Do demons always attack this place?" Rhodes asks

"Sometimes they attack." Carmack looks back to them "How else am I going to find subjects for my work? Can you men dispose of them? Take the mind control grenades; I only have a few so make it count. Go target the big ones for me."

Doom looks to Rhodes and lends him the spiked orb he was holding on, handing him the mind control grenade while another Crusader takes the other one from the open briefcase. "We'll take care of the demons."

"There are two cyborgs outside, watching the gate. I can send the demons out so you could see what they are capable of."

"There's no need… Let us handle this." Rhodes looks at the Crusaders "Let's move Crusaders."

The squad take their leave by going through the door they went through before, just when Doom was about to leave too, Carmack intervenes. "Doom Slayer… Can I see you for a moment… I need to show you something."

Doom stops and looks at Carmack, he turns to Rhodes, seeing him and the Crusaders looking back at him. "We'll take care of the stragglers." Rhodes said "We'll be back."

The Crusaders double time on jogging the way outside, getting their weapons ready and looks up at the sky, seeing a few Cacodemons, Warlords and Lost Souls, flying closer to the Sanctuary. The Crusaders spread out around the entrance, aiming their weapons and open fire, shooting them down before they get closer. The cyborgs join in the fight, firing their plasma rifles, shooting down the Warlords and Cacodemons.

Inside the Sanctuary, Doom Slayer follows Carmack through the corridors, taking him somewhere in the facility. Doom stays behind Carmack and looks to the right when seeing window screens on the sides of the corridors. Through the window screen was a Baron of Hell walking around, it turns its head towards Doom but did nothing about it, just keeps walking. One thing that got Doom's attention and got him to stop was looking straight towards a large tube that was in the center of the room, filled with orange water but inside was a Baalgar Demon itself, sleeping stasis inside this pod.

"You enjoy killing these things don't you?" Carmack asks, standing next to him, getting Doom to look to him while Carmack looks through the window screen "That thing in there is difficult to control; I haven't tried to control something that big." He looks back to Doom "Don't you like to make the demons kneel before you?"

Doom remains silent and looks back through the room, looking at the Baalgar Demon in the stasis pod. He looks away and moves forward, walking through the next room with Carmack following him from behind. Inside he could get a good look at many artefacts, relics and stone statues, all ancient histories of his past in Argent D'Nur. Doom stays at the front entrance, looking at all the ancient artefacts while Carmack walks through, walking past a Hell Knight that stood by the side. Doom follows Carmack but stops and walks towards the Hell Knight, standing face to face with this demon, looking at the Hell Knight while it looks back at him. The Hell Knight remains where it stands, not attacking or do anything to him; the Hell Knight would soon depart from the room when Carmack orders it to do so, asking it to leave.

Meanwhile, outside the Sanctuary, the Crusaders move back inside when the Warlords made it to the ground and moves further within, the two cyborgs would remain where they are but one got eaten by a Cacodemon while two Lost Souls blew the other one up. The Crusaders held a defensive position inside the room, firing their weapons and killing the Warlords quickly. Only a few Warlords remain and continues throwing fireballs at them, the Crusaders kept holding and threw grenades back at them, blasting them out of the room. They gain the victory and sustain no deaths, only injuries from fireball damage when they fled inside the building.

"Targets neutralise." One of the Crusaders said

"Watch yourselves." Rhodes said while reloading his weapon, moving out of cover and moving closer to the dead Warlords "Can't afford to deal with any stragglers."

"You didn't use the mind control grenade." One of the Crusaders said, moving out of cover and follows Rhodes and the others as they too came out of cover

"The demon that would be on our side wouldn't last long." Rhodes said while aiming his weapon at the bodies, seeing them all disintegrate, leaving no trace of any of the demons here. Once he made it outside, seeing no more demons, he lowers his weapon and sighs relieved. "All clear."

"Not clear." Said one of the Crusaders, standing nearby and pointing out at the top of the cliffs.

A UAC Blackhawk came flying over the cliffs, making its way straight towards the Sanctuary inside the Blackhawk was the same team from Firebase Bravo, Sergeant Travis and Lauren and the rest of the UAC marines. Corporal Rhodes and the Crusaders stay together, looking at the Blackhawk as it comes flying down closer to them. Once it gets closer, it makes a landing, landing on the ground for the marines to come out and start moving towards the Crusaders, once they are out, it takes flight and flies out of here.

"Crusaders!" Sergeant Travis calls to them, lowering his weapon and taking off his helmet, showing his face to them

"Corporal Rhodes. What are you guys doing here?"

"We got orders…" Lauren steps forward, holding onto her sniper rifle with both hands "The UAC command ordered us to come here and retrieve high value research into biologic weapons against the demons."

"Yeah we know… The whole mind control against demons."

"What?"

"Get in line…" Rhodes turns back "I'll explain it along the way."

Back inside the facility, Doom walks around a few of the relics, looking at these large floating stone tablets with markings all over it. He stares at three flat tablets, seeing himself on the middle one, standing on the edge of the cliff, holding a strange cube in one hand while having his other arm grabbed by the demons that are crawling their way to him up the cliff.

"I found these tablets from Mars and the old Mars city. This is probably what is left of the ancient histories of the legendary Doom Slayer." Carmack said "I know all about as much as I can, all about the days of you, walking through the bloodied path with your guns and your thirst for brutal carnage wherever you go. I know all about the time when you found them, the ancient human civilisation that lived in another world. They are known as the Night Sentinels correct?"

Doom turns his head to Carmack when he mentioned the Night Sentinels. Carmack stands where he is, smiling while looking back at him but he turns to the side "There is something I want to show you."

Carmack takes Doom into another room, a darker room with little light to show where he is. Carmack stays outside, monitoring the area from where he is, staying by the computer and watching Doom on the camera that is in the corner of the wall. Carmack would turn away when hearing Corporal Rhodes returning, seeing he brought the UAC marines with him too, making him joy when seeing them here. He gets off the chair, walks up to them, greeting them all, and begins explaining to them the same information he told the Crusaders.

Doom moves further within the room, he still cannot see a thing as only a faded light is above the ceiling. He moves above the light, there he looks straight ahead and seeing someone, seeing someone sitting there on the floor against the wall but that person got up when getting a look at Doom. This person calls out his name "Doom Slayer." And starts moving closer to the light but still cannot see him yet. The man says to Doom "It has been a long time… Since I saw your face." He spoke in a darker voice.

Doom stands his ground, waiting for this shady character to come closer so he can get a look at him. He soon turns his head to the right, noticing a steel table against the wall, on the table was a few folders, a glass cup of water and a jug. Something else was on the table that got his attention; he turns towards the table and walks closer, seeing a dark black helmet that belongs to the Night Sentinels. The helmet was a darker black and greyish colour instead the proper white and silver, he was about to move his hand towards it but the shady character calls out "You don't want to touch that, Doom Slayer."

Doom looks back at him, seeing him move closer until finally Doom could get a look at him, seeing he is a Night Sentinel. The man wore the Night Sentinel armour but it was all a black and greyish plated armour, he cannot see his face but could see his teeth that is sharp like the demons, seeing his skin underneath the armour is all purple flesh like the demon soldiers. This demon surprised Doom, surprising him to step back while the demon stands there looking back at him. Doom looks back at the helmet and places his hand over it; there he begins to see vision of the past of this Night Sentinel, revealing who he really is.

The past of the Night Sentinel, showing visions of battles against the demons, seeing himself sometimes, fighting against the demons with his Night Sentinels by his side, fighting against them with the Crucible. The Night Sentinels stays back and supports him, having two drawing swords while the other two held onto long rifles, firing blue energy beams through the demons. One of the sentinels with the rifle was the one standing in the room with the Doom Slayer, firing his rifle at the demons, taking a few head shots at the Imps. He soon gets company with a Mancubus that was nearby, both he and the other sentinel with the rifle turns to the right and starts shooting at it a few times. The Mancubus fires with four fireballs, the two rolled to the side, avoiding those shots. The sentinel threw a grenade, sticking the grenade onto the chest then explodes, removing a large chunk of the Mancubus, having its organs fall to the ground.

The next vision takes place elsewhere, seeing this Night Sentinel moving through a demon corridor, looking down at two dead Night Sentinels on the ground, both torn apart by the demons. He moves up ahead and finds one more sentinel stuck against the wall, having a long blade through the chest, making him rush towards him and pull him down. He held onto this sentinel with both arms, holding onto him and mourning over his dead. While he mourns for his death, someone else came nearby, standing by his side, covering himself in dark brownish robes.

The shady figure speaks to the sentinel "I can resurrect your son if you want him back." The man said, getting the sentinels attention when he looks up at him

The sentinel took out a handgun and takes aim at the human "Who are you?!"

The shady figure raise his head up, showing his face, showing his pale skin with some parts torn off and dark orange eyes. The man responds "You can call me Deag Grav."

"You're a Hell Priest." The sentinel said

"Indeed I am. I can help you, you know." Deag Grav said "Your son, alive and well in your arms. If you wish for him to return, you shall do something for me."

The sentinel shakes his head slightly; he looks back at his dead son while Deag Grav sighs "Very well then…" He turns around and walks away "You will never see him again."

The sentinel held onto him, still thinking about and his temptations took the better of him. He looks back out, calling out "Wait!" His call got the Hell Priest to stop.

Deag Grav turns around and looks back to him "Do we have a deal?"

The sentinel drops his gun and lowers his head when looking towards him "What do you want?"

The deal struck. The Night Sentinel accepted the deal, which brought the downfall to the Night Sentinels of Argent D'Nur. The Night Sentinel brought the Hell Priest to the Elemental Wraiths; here is where he changes everything, changing the Elemental Wraiths as well as ending the war. The Hell Priest used his dark powers to control the Elemental Wraiths, there he created a beam to merge all three together in the center, once together, they fire into the sky, hitting the sky and creating a crack, breaking down the walls between worlds. This would eventually create a large crack in the sky, on the other side was Hell itself, slowly breaking the sky and bringing this world to the other.

The Night Sentinel who brought Deag Grav here witness the end to Argent D'Nur, still he wishes to see his son. "Where is he?" The sentinel asks him, standing behind Deag Grav, waiting for him to respond

"Oh yes… Your dear son." Deag Grav would raise his hand up at the sky, pointing towards the crack in the sky.

In the sky above Argent D'Nur, something was happening to the crack in the sky, something on the other side grabs a hold of it and tries to make it bigger, seeing four white arms grabbing both sides of the breach, opening it right up to reveal itself to the Night Sentinels. They have never seen this demon before, a large white demon with a huge goat-like head and white eyes with no pupils. There was a round red circle on the forehead, soon to glow while this demon talks in demon language but was actually speaking backwards.

"Isn't it magnificent?" Deag Grav said, looking at the white demon in the sky "It is the icon of all of your sins."

The demon lets off a terrible screech across Argent D'Nur for everyone to hear, once it stops screeching, its forehead starts shooting out orange flaming cubes, sending waves of these cubes down at the city. On impact, these cubes transform into demons, all different kinds of demons except for the rare and soldier ones, these demons would be spawn and they begin unleashing hell across this city. The Night Sentinels and the people panic in fear, seeing the demons are inside the city, they try to defend themselves against the demons but they have no more power, their powers are gone and their swords are no match against them. They revert to weaponry but more demons keep coming, the white demon in the sky continues spawning more demons, eventually overwhelming their military power.

"No…" The Night Sentinel said, looking at the city as it lights a flame. He looks back at Deag Grav and takes out his handgun "This is not what I had in mind. You lied to me!"

Deag Grav turns around and unleashes orange essence from his hands, sending them straight inside the sentinel's body. He drops his gun and spreads his arms out, shouting in pain while this magic is turning him. Deag Grav would explain before he turns "What would be the point of bringing him back just to watch him die again when this world burns. He is better off a demon on our side, that way he can help destroy this world, and it is all thanks to you. You will be remembered as the Betrayer, the one who doomed the Night Sentinels."

The vision ends here when Doom backs away from the helmet, it fell to the side and fell off the table while Doom stands there, watching it happen. He turns his head towards the sentinel, realising that he is the Betrayer. He responds with all of this by killing him, drawing out his double barrel and fires, firing at close range but something stopped him, a strong bulletproof glass wall was in between them. The shells bounce off the glass wall and hits Doom instead but that did not damage him, he only flinched. Once he notice there is a glass wall in front of him, he drops the double barrel and punches the glass wall twice, getting only a slight damage to it.

"What the hell is he doing?" Carmack said, watching Doom punching the glass wall

"Who the hell is in there anyway?" Rhodes asks

"He is a Night Sentinel." Carmack said "He was found by my associates. He told me everything, everything I need to know about the demons, his world, the Doom Slayer… Everything."

"Doesn't look like those two are friendlies." Lauren said, still watching the screen, watching Doom punch the glass wall a few times until finally stopping.

"Let it all out." The Betrayer said looking at him as Doom looks back at him "I deserve a thousand deaths after what I have done to my kind, for that I must remain as a demon. Now that you are here, can we finally talk? I have something that you need, something that you have been looking for, for a very long time."

Doom Slayer stands where he is, still breathing heavily after finding out that he is the Betrayer. He stays where he is for the time being, he finally moves by raising both hands up, grabbing both sides of his helmet.

"Oh my god…" Rhodes said, moving closer to the screen "He's taking off his helmet."

"We can't see his face anyway in that dark room." Lauren said then looks at Carmack "Can you fix that?"

"I can't." Carmack said

"Oh that's just great." Rhodes said while moving away from the screen

Doom takes off his helmet, dropping it onto the floor, revealing his face to the Betrayer while everyone else in the other room that is watching the screen could see the back end of his face. The Betrayer says "Now that is a face I haven't seen in a long time."

Doom Slayer would suddenly respond to that, finally speaking out for him and everyone else in the other room to hear. "Hello. Betrayer."