Color drains from his face and he takes a step back, but the action looks more like someone pulled the feet from under him.

"No, no, no. He didn't do anything wrong."

"I know that, child. But there was nothing that could be done with the magic of this world. However, the introduction of your magic into the equation has opened what I believe to be another way. I would need you to help me, but I believe now that what I seek can be accomplished without Ari's death."

She takes Henry's hand in her own. "What would you do to keep Ari alive?"

"I would... I would die for him if necessary." He is actually surprised. He is aware that he has known Ari for a short while.

But he would die for him, yes. It's plain in his face.

"No one will die here today," she smiles. "Follow me."

She opens the door back into the armory proper and heads outside to the roof.

Henry follows, feeling like someone just dumped a bucket of cold water on him. "What do you have in mind?"

Ari is already standing outside with the Stone, shaking with the effort of keeping its power contained.

"You will transfer Ari's 'youth' to me. I will use that connection to drain his demonic power into myself, then I will sacrifice myself to destroy the Stone. I've already drawn up the diagrams."

"Okay. I am so sorry." He will cast the ritual according to the instructions.

The ritual involves rather a lot of black-and-red demonic magic, flowing through the air sluggishly like blood mixed with oil. Speaking of blood, there's a very large diagram drawn in it. It's not clear where Adria got all that blood.

The youth-siphoning connection between Ari and Adria quickly becomes visible, more black and red flowing from Ari into his mother. It looks like he's dwindling away, his body growing slim and his hair lightening until he barely looks like himself, just some bony, white-blonde youth. Adria, meanwhile, grows taller and stronger, until she hardly looks human.

The Soulstone shudders violently throughout, red lightning crackling along its surface. At the climax of the ritual, once Adria has grown to her full height, it shatters into dozens of tiny pieces.

Ari pants. "Is- is that it? Did we do it?"

"Not yet, my son," Adria says.

The shards of the Soulstone tremble, then, in one sudden movement, they bury themselves in Adria's forehead.

She laughs as she grows even taller, even stronger. Her skin reddens, spines push through her skin, and her eyes glow with hellfire. Then she gestures, wrapping Ari and Henry in thick black chains.

"Dear, sweet Ari," the creature says mockingly. "You truly thought old Adria was on your side, didn't you? That after abandoning you to the care of that old fool, she had returned to make everything right again? No, no. She only ever served me. And now, through her great work, I am reborn, greater than ever. The Seven are as one within me, the Prime Evil!"

"No!" Henry pushes his anti-magic against the Prime Evil.

The chains waver for a moment, but Diablo grunts and they’re replaced by a tight cage of that same demonic bone from the Arreat Crater. The Prime Evil turns her gaze on Henry. “I must thank you, Henry. Without your aid, I could never have reached the height of power I have now achieved. And now, I will get what I have craved for so long: the utter destruction of the High Heavens!”

She turns away and rends the air itself into a massive red portal which floats above the ground, bleeding streamers of demonic energy into the sky. She steps through, but the portal remains open. 

Li-Ming runs onto the roof moments later. “Is it done? I- what the fuck happened here?”

"Adria... Adria betrayed us. She turned into Diablo."

"It's my fault. I need to fix this."

"Fuck. I should have known, I thought she was suspicious, but she was our only option- Lorath, get up here, Henry's in some kind of bone cage-"

Lorath comes up the stairs, looking grim, and gestures at the bone spires keeping Henry caged. They bend open reluctantly. "Are you okay?"

He's followed up the stairs by Tyrael, who looks thunderstruck. "Where... where does that portal lead?"

Henry climbs out of the cage, trembling.

"Hell." It might either be an expression or an answer to Tyrael's question. "Ari, someone help Ari."

"What happened?" Felix says suddenly.

A second later his brothers are there too.

...so, is Gabe, next to Henry.

"What the fuck..." he looks around, notices who is not here. "Is Adria to blame for this?"

Ari's chains have already vanished, but he's on the ground and he doesn't seem able to get up. "I... I think the portal leads to Heaven. Adria... took my demonic power and consumed the Seven Evils. I feel so weak."

Tyrael goes ashen and runs through the portal before anyone can react.

Sorcery magical lifeforce analysis circle appears to manifest itself near where Ari is. Also, Henry and Gabe are standing next to Ari. So is Felix.

"You three should stay here, figure out how to help Ari. " Felix turns to the others. "We should go quickly."

"Agreed. Through the portal, then."

Li-Ming steps through, followed by Lorath.

The analysis reveals that Ari has been depleted of almost all his life-force except breath, which has practically doubled. He almost seems to be composed of breath alone.

Okay, there must be something that they can do.

The triplets go through the portal.

Through the portal, there is a heavily wounded angel, who is yelling at Tyrael. There's also a wall, off in the distance, which used to have a gate in it but currently does not, as the gate in question is currently lying in splinters on the ground. Demons swarm through the space where the gate once was. The city beyond it is in flames, with angels battling demons in the streets.

The angel continues to berate Tyrael. "The Heavens burn. This is your fault, Tyrael. The Diamond Gates have stood since the light first broke over the High Heavens. Now they lie in ruins. You are the cause." He turns and vanishes in a plume of flame. Tyrael sinks to his knees.

"Diablo did this, not you," Li-Ming says. "You did everything in your power to prevent this."

"Long ago," Tyrael says dully, "my brethren and I voted to decide the fate of humanity. I cast the final vote that spared you from extinction. Now... humanity has birthed the Prime Evil."