"Horcrux," Sirius said.
The word landed in the room the way such words do. Not loud or dramatic but with the weight of something that has been carried a long time and has finally been set down on a surface between two people.
Regulus went very still.
Not surprised. Sirius could see that immediately — the stillness wasn't the stillness of shock but of recognition, of a word arriving that had been expected and dreaded in equal measure for a very long time. He knew the word. Of course he knew the word. He had gone into that cave because he knew the word.
"The locket," Regulus began.
"Kreacher has it. He's kept it safe since — since you sent him home." Sirius watched his brother's face carefully. "You didn't fail, Reg. You just didn't finish."
Regulus looked at his hands on the sheets. "Those aren't the same thing."
"No," Sirius agreed. "They're not."
The silence held for a moment. Outside the window the light had the quality of mid-afternoon, grey and steady above the water.
"How many," Regulus said. Not a question exactly. The tone of someone checking their own information against another's.
"We don't know for certain. The goblins confirmed the locket. Beyond that—"
"Seven," Regulus said quietly.
Sirius looked at him.
"He was obsessed with the number." Regulus's voice had gone flat and clinical in the way it went when he was describing something he had already processed as much as it was possible to process. "I heard things. Fragments. He believed seven was the most powerful magical number, that splitting a soul into seven pieces would make him — he used the word invincible." The word came out like something distasteful. "I don't know how many he had made by the time I — by the time the cave. But seven was always the number."
Sirius absorbed this. "That's more than the locket."
"Yes."
"So, there might be more."
"There might be others, yes," Regulus confirmed. He looked up. "That's why you need to tell me whatever else it is you're not saying yet. Because I can see that you're not finished and I'd rather have all of it at once."
Sirius leaned forward in the chair again. His elbows on his knees, his hands loosely clasped, looking at his brother across the small distance of everything they had just said.
"What are your plans?" he asked. "When you're well enough. What were you going to do?"
Regulus didn't hesitate. "Destroy it. Find a way to destroy the locket and whatever else he made and finish what I started." He said it with the quiet certainty of someone for whom this had never been a question. "I went into that cave with a plan, Sirius. Waking up somewhere warmer doesn't change the plan."
"I know." Sirius looked at him for a moment. "I need to tell you something first. About the children."
Regulus waited.
"Not my children," Sirius said. "Not yet. The Potters'."
Something shifted in Regulus's expression. Carefully neutral, the way he had always gone carefully neutral when a conversation was moving somewhere he wasn't certain he wanted to follow.
Sirius told him.
He told him about Dumbledore. About the night Voldemort fell and what had happened in the aftermath, the decisions made in an office at Hogwarts while the wizarding world celebrated outside. About James and Lily and the choice they had made, or been guided into making, or both. He told him about two small boys left with Muggle relatives in Surrey. What those relatives had done with them. The cupboard. The years of it. The state they had been in when Marius found them.
Regulus said nothing through any of it.
That was the thing about Regulus — he had always been able to hold very still while absorbing very large things. He had learned it young, in a house where showing the wrong reaction at the wrong moment had consequences. But Sirius knew how to read him and what he saw underneath the stillness was not the cold fury of someone hearing something that confirmed what they already suspected. It was the quality of someone encountering something genuinely incomprehensible. Something that didn't fit any existing category.
"The Potters," Regulus said finally. His voice was very even. "James and Lily Potter."
"Yes."
"Who you fought beside for years."
"Yes."
"Who you would have done anything for."
Sirius said nothing.
Regulus looked at the ceiling. "I made terrible choices," he said. "I joined a movement that tortured and murdered people and I believed in it, at least for a while. I am not going to pretend otherwise." He paused. "And I still find what you've just described to me difficult to comprehend."
"I know."
"Their own children."
"I know, Reg."
Regulus was quiet for another moment. Then — "You said my children. Earlier. When I asked." He looked back at Sirius with the expression of someone who has noticed a thread and intends to follow it. "Those boys. They're yours now."
"They're mine," Sirius confirmed. "All four of them. There was a ritual. A blood adoption." He paused. "It's a long story."
"You seem to have accumulated several of those."
"I have." Sirius looked at his brother steadily. "The woman who performed the ritual with me. Who made it possible. She's a healer. One of the best in the world, actually." Another pause, shorter. "Her name is Esme."
"Your wife."
"My wife."
"Esme," Regulus repeated, with the tone of someone trying a word out for size. "What's her surname? Her family name?"
Sirius looked at him.
"Malfoy," he said.
The room was very quiet.
Regulus looked at his brother for a long moment. Then something happened to his expression that Sirius hadn't seen in a very long time — the almost-smile from earlier returning, but fuller now, with something genuinely delighted underneath the exhaustion.
"Malfoy," Regulus said.
"She's estranged from—"
"Sirius Black," Regulus said, with the quiet wonder of someone witnessing something they could not have invented, "who told me at fourteen that the Malfoys were everything wrong with wizarding society—"
"She's nothing like—"
"—married a Malfoy."
"If you could just let me—"
"Of all the witches," Regulus said, softly, to no one in particular, with the specific appreciation of a man who finds the universe's sense of humor genuinely impressive, "in the entire world."
"Hey," Sirius said.
Regulus looked at the ceiling with the expression of a man storing something away for future use. "I'm simply observing."
"You're enjoying yourself."
"I've been at the bottom of a lake," Regulus said serenely. "I'm allowed."
Sirius shook his head. The expression underneath it was not irritation. It was the expression of a man who has his brother back and is finding, against all expectation, that his brother is exactly as he remembered him.
The smile faded from Regulus's face on its own, slowly, the way it had before — not because anything had been said but because he had been watching Sirius's expression and he knew that face. The same tell it had always been. The look of a man who hasn't finished.
"There's more," Regulus said.
"There's more," Sirius confirmed.
He said it plainly, the way he had said Horcrux — without preamble, because Regulus had asked for all of it at once and he was going to give him all of it.
"My eldest son," Sirius said. "Rigel. Before the adoption his name was Harry. Harry Potter."
Regulus went still again. A different stillness this time.
"Charlus's brother," he said slowly. "One of the boys you just told me about."
"Yes." Sirius held his brother's gaze. "He was in that nursery on Halloween. When Voldemort came." A pause. "The curse didn't hit Charlus, Reg. It hit Harry. The rebounded curse — the one that destroyed Voldemort's body — it came from Harry. Not Charlus."
The silence stretched.
"The prophecy," Regulus said. Very quietly.
"Was always about Harry. Everyone looked at the wrong boy." Sirius pressed his mouth together briefly. "Dumbledore. James and Lily. All of them. They assumed. And then they discarded the actual child of prophecy because they had already decided he was a squib and sent him to Surrey and—" He stopped. Reset. "It was Harry. It was always Harry."
Regulus said nothing. He was very still in the way he had been still when Sirius said Horcrux — the stillness of a mind moving very fast toward a conclusion it had not yet reached but could already see from here.
"The curse," Regulus said. "When it rebounded. When it hit him." His voice was careful now, deliberate, picking its way through the logic of it with the precision of someone who understood the magic involved better than most. "A soul that has been split — when the killing curse rebounds from something it cannot kill—"
"It left a piece of itself behind," Sirius said. "In the scar. The goblins confirmed it during the adoption ritual. It's contained now. The adoption — the ancient magic in the ritual — contained it. But it's there."
Regulus closed his eyes.
He kept them closed for long enough that the light through the window shifted — a slow, almost imperceptible change, the grey of the afternoon beginning its movement toward the grey of early evening. Sirius did not rush him. He sat in the lopsided chair and waited and watched his brother's face and said nothing.
When Regulus opened his eyes, they were very dark and very clear.
"He made a Horcrux by accident," Regulus said. "Voldemort. He doesn't know."
"We don't think he knows. No."
"Which means his count is off. Whatever number he thought he was working toward — he has one more than he intended." Regulus looked at Sirius with the expression of someone filing information that is both crucial and terrible. "He'll be looking for it eventually. When he comes back. He'll feel the absence of it, and he'll look for it and he'll find—"
"A child," Sirius said. "I know."
"Your child."
"I know, Reg."
The weight of it settled over them both. Not new information — Sirius had been carrying it since the vaults, since Ragnok's careful voice delivering careful facts in the deep quiet of Gringotts. But saying it aloud in this room, to his brother, to someone who had been inside that world and understood what Voldemort was in a way that even Sirius with all his years fighting him had never quite managed — it landed differently. More specifically. More real.
"I'll find a way," Regulus said.
Sirius looked at him.
"Extracting a Horcrux from a living person," Regulus continued, in the flat clinical voice that meant he had already decided something and was now simply explaining the decision. "It's never been done. There's no record of it because the people who make Horcruxes don't generally put them in living people intentionally and nobody has survived being an unintentional one long enough to—" He stopped. "There's no precedent. But there's the locket. And there's the library at Grimmauld. And there's everything I know about how he made them and what he used and why." He met Sirius's eyes. "I'll find a way."
"Reg—"
"I went into that cave to destroy one Horcrux," Regulus said quietly. "I'm awake. I have time. The least I can do is finish what I started."
Sirius looked at his brother for a long moment. At the thin face and the dark eyes and the absolute quiet certainty in them. The same certainty that had sent him into a cave alone. The same certainty that had kept him breathing at the bottom of a lake for five years on nothing, but sheer stubbornness and a task left undone.
"You'll stay at Grimmauld," Sirius said. It wasn't quite a question.
"The library is there. The warding is there. Nobody expects a dead man to be living in a Black estate." Regulus looked at him steadily. "And the Horcrux needs to stay away from the children. Both of them. The locket and—" He stopped. "Rigel doesn't need that thing anywhere near him."
"I could ward Blacktide—"
"Sirius."
"I know," Sirius said. He did know. He had known before he suggested it. "Grimmauld."
"Grimmauld," Regulus confirmed. "And nobody knows I'm alive. Not yet. Not until we understand more." He paused. "Voldemort's loyalists are still out there. Scattered but not gone. If they knew—"
"They won't." Sirius held his gaze. "You have my word."
"And the children," Regulus said. "The truth about them. That stays with me."
"Yes."
Regulus nodded once. The nod of someone who has made an agreement they intend to keep, which was the only kind of agreement Regulus had ever made.
The room had grown darker around them. Neither of them had noticed the light going — had been too far inside the conversation to mark the slow shift of afternoon into evening, the grey at the window deepening by degrees until the room was lit more by habit than by anything coming through the glass. The North Sea outside was invisible now, only audible, the tide doing what it always did regardless of what was being decided in rooms above it.
Sirius looked at the window. Then at his brother.
Regulus was looking at his hands again — steadier than they had been when he first woke, the soreness of a body remembering itself already beginning to settle into something more manageable. He looked thin. He looked tired. He looked, underneath both of those things, like someone who had been given a reason to get up in the morning and had already started thinking about how to use it.
"I should tell Kreacher you're awake," Sirius said.
Regulus looked up. Something crossed his face that was not quite the almost-smile but was related to it — something quieter and more private. "He'll be insufferable," he said.
"Completely," Sirius agreed. "He's going to cry."
"He doesn't cry."
"He absolutely cries. I've seen it." Sirius stood from the lopsided chair, his joints registering their protest at the hours he had spent in it. "He's going to cry and then he's going to tell me it's all my fault somehow and then he's going to make you tea and hover until you drink all of it."
Regulus looked at him. The almost-smile had arrived properly now, thin and real and pulling at the muscles that were still relearning how to do it. "That does sound like him."
"It does." Sirius looked at his brother — at the lined face and the dark eyes and the person sitting in the bed in a room above the North Sea who had been at the bottom of a lake and had come back anyway. "Rest tonight. We'll figure out the rest."
Regulus held his gaze. "Together," he said. Not a question. Not quite a statement. Something between the two — the careful offering of a word that had not been available to either of them for a very long time.
Sirius looked at him for a moment.
"Together," he said.
He went to find Kreacher.