The stone walls of Number Twelve, Grimmauld Place gleamed cold in the gathering dusk, and deep within the old house lingered a heavy scent of dust and aged wood.
The embers in the fireplace had dwindled to a few faint sparks, casting the shadows of three figures long and short in turns.
Sherlock's face was still somewhat pale, the cold sweat at his temple not yet fully dry.
Dumbledore, worried that the boy's weakened state might alarm the Holmeses and Hermione back at King's Cross, had simply Apparated both of them directly to the Black family's ancestral home.
Sirius knew nothing of this—at this very moment, he was still at the Holmes residence playing Wizard Chess with Holmes, patiently awaiting their return.
"Sir, shall I summon Sirius back?" Harry asked, his gaze resting on Sherlock's pallid profile, his voice edged with concern.
"Not yet." Dumbledore shook his head slowly, his silver beard swaying gently with the motion. He turned, the blue eyes behind his half-moon spectacles warm with care, and looked toward Sherlock, who was leaning against the sofa. "How are you feeling now?"
"Much better." Sherlock's voice still carried a faint rasp. He shifted his posture, settling deeper into the sofa back to let his body stretch more comfortably. "Quite enough left in me to see this through with you."
"You know what I intend to do?" A flicker of curiosity crossed Dumbledore's eyes.
"Self-evident, my Headmaster." Sherlock's gaze drifted to the pocket of Dumbledore's robes, where the outline of something small pressed faintly against the fabric.
"We drank that scalding potion in the cave—cup after cup—then spent every last effort destroying over a hundred Inferi, all to retrieve Voldemort's Horcrux. The journey back was no place to examine it, but now—"
He paused, his fingertips tapping lightly against his knee. "It is time we had a proper look at another of Voldemort's Horcruxes."
At Sherlock's words, Harry went utterly still.
He opened his mouth, eyes flooding with sudden realization and dismay.
Because he had forgotten. He had completely forgotten the most important thing of all.
What had they been running about all day for?
To find the Horcrux. That was why.
Back in the cave, watching Sherlock drink that terrible emerald potion cup by cup, watching the colour drain from his face and his breathing grow ever shallower, Harry's mind had held only one thought:
'Sherlock cannot die.'
After that, it had been finding water for Sherlock, then watching Dumbledore fight off the Inferi and the matter of the Horcrux had been swept entirely from his mind.
"Understandable, Harry." Dumbledore's voice carried a gentle smile. He reached out and laid a hand lightly on Harry's shoulder. "You are too kind-hearted. You always think of others first."
Dumbledore's words eased much of the guilt from Harry's chest. He scratched the back of his head, a little sheepish. "But sir—when did you… put the Horcrux away?"
"At the moment Sherlock finished the last cup, and the Horcrux surfaced from the bottom of the basin." Dumbledore spoke slowly as he reached into his inner robe pocket and drew something out.
It was a golden locket, gleaming with a cold light in the dimness of the room. "Your attention was entirely on Sherlock's condition—you didn't notice. So, I slipped it away."
"The locket!" Harry's eyes lit up at once. He leaned forward two steps, barely containing his excitement. "The one from the Pensieve—the one that witch had in her collection! Slytherin's locket!"
The moment he saw it; the memory came rushing back. He and Sherlock had watched alongside Dumbledore through the Pensieve, following the house-elf Hokey's memory. Tom Riddle—not yet Voldemort—had visited a pitiful witch named Hepzibah Smith, who had shown him two treasures from her collection: Helga Hufflepuff's golden cup, and Salazar Slytherin's locket.
And what Dumbledore now held was Slytherin's locket.
Both Harry and Dumbledore wore expressions of barely-contained excitement. Harry's hands balled into fists at his sides.
The ordeal in the cave had been agonizing—Sherlock had nearly died—but at least it had not been for nothing. They had the Horcrux. Finally.
Yet when Sherlock's gaze passed over the locket in Dumbledore's hand, one eyebrow lifted subtly.
The potion's aftereffects had largely worn off now, and his eyes had regained their usual sharpness.
His meticulous powers of observation caught the wrongness in an instant.
But it was only a deduction—so he said nothing.
What happened next, however, confirmed it precisely.
Dumbledore drew a slow breath, pressed his fingertip lightly against a small raised catch on the locket's side, and pushed. A soft click—and the lid sprang open.
The smile on Dumbledore's face froze.
He stood completely still.
The locket was empty.
The truth was, back on the rocky island, Dumbledore had been too preoccupied with Sherlock's state to examine the locket closely. But when he had taken it from his pocket just now, a vague unease had crept over him.
A locket must hold something inside. The moment it was in his hands, he had sensed the weight was wrong—too light.
The thought had passed through his mind like a shadow and vanished before he could hold it.
Until now, when the lid came open and that wrongness surged back, stronger than before.
He was certain, at least, that there had been only this one thing in the stone basin.
"Sir?" Harry noticed Dumbledore's expression go grave. He asked carefully.
Though Sherlock could not see inside the locket from where he sat, understanding surfaced in his eyes. His tone was perfectly calm. "Empty?"
"What?" Harry's eyes went wide. He crossed quickly to Dumbledore's side and peered into the locket—and it was, indeed, hollow and bare.
Dumbledore gave a faintly self-mocking sigh. He extended one finger and brushed it across the inside of the locket.
"Not entirely empty. There is this." He reached into a small inner compartment—made for holding a miniature portrait—and drew out a folded square of parchment, carefully creased. His fingers opened it slowly.
The handwriting was hurried and uneven:
To the Dark Lord
I know I will be dead long before you read this, but I want you to know that it was I who discovered your secret.
I have stolen the real Horcrux and intend to destroy it as soon as I can.
I face death in the hope that when you meet your match, you will be mortal once more.
R.A.B.
A brief silence settled over the sitting room. Only the faint crackle of dying embers.
"Sir?" Harry called again, softly, his eyes fixed on the parchment, full of confusion.
Dumbledore said nothing. He only passed the parchment quietly to Harry.
Harry scanned it—his pupils contracted sharply and immediately handed it to Sherlock.
Compared to Harry and Dumbledore, still submerged in shock, Sherlock was considerably more composed. He took the parchment, ran his fingertips across its surface to feel the texture of the paper then held it up toward the light.
Then he glanced at Harry, who was still staring blankly, and said with perfect calm, "Would you mind fetching the locket as well, dear friend? Thank you."
Harry, in this moment, was like a puppet on strings—Sherlock spoke, and he moved. He took the locket from Dumbledore and handed it over, his movements still carrying a trace of dazed stiffness.
Sherlock took the locket, weighed it gently in his palm, then brought it close to examine the carvings along its body. His fingertip traced the engraved lines as he spoke, voice crisp and analytical:
"Compared to the locket we saw in the Pensieve, this one is slightly smaller. There is no Slytherin S-serpent sigil anywhere on the case, and the workmanship is considerably cruder."
He tapped the parchment.
"The paper itself is common stock—mass-produced, the sort sold at any stationer's on Diagon Alley, found in almost every wizarding household. The handwriting, however, belongs to someone in a state of considerable agitation—the ink blots and the erratic strokes both attest to it. Though the written content makes that rather more plainly evident."
He paused, and something like genuine admiration flickered in his eyes. "Stealing the real Horcrux from right under Voldemort's nose, and leaving a note like this behind. A remarkably clever individual."
"But why?" Harry finally snapped back to himself, and the questions came tumbling out in a rush: "Why did someone take it? Why would anyone put a fake in its place? Where is the real locket now?"
"None of it is impossible," Sherlock said evenly. He set the parchment and the locket on the low table and leaned slightly forward. "If we were capable of reaching that cave, so was anyone else—provided they knew Voldemort well enough, and had sufficient courage."
"Be calm, Harry." Dumbledore's hand pressed gently onto Harry's shoulder. He looked into Harry's eyes, his voice steady. "At the very least, we now know that this R.A.B.—whoever took the real locket—was on our side."
The weight of Dumbledore's palm helped settle Harry somewhat, but three questions still tumbled from him: "But who is he? And why did he take the locket? And—has the Horcrux actually been destroyed?"
Dumbledore was thoroughly overwhelmed by the volley of questions.
In reality, the only reason he managed to hold his composure at all was decades of hard-won experience. Because inside, the disappointment was impossible to suppress entirely.
Finding this hiding place had cost him an immense amount. And what had just been endured to retrieve the locket—what it had cost Sherlock and Harry filled him with a guilt he could not set aside.
To discover, after all of that, that it had ended like this.
Undeniably, Harry's three questions were precisely the three questions Dumbledore most wanted answered. Especially the identity of this mysterious R.A.B.
Dumbledore drew a long breath and pushed the feeling down. His gaze turned to Sherlock, the steadiest of the three. "Sherlock—what do you make of it?"
Sherlock looked at Harry beside him, his tone easy. "Harry, I rather thought you'd know the answer."
"Me?" Harry pointed at himself, startled. "Why me?"
"Indeed." Sherlock's gaze shifted toward the staircase leading to the upper floors. "You'll remember, I imagine, that Sirius once showed us the Black family tapestry?"
Harry nodded at once.
That black tapestry, hanging in the upstairs drawing room—the names of every Black in every generation embroidered across it, and the scorched holes where the burned-away members had been blasted off. It was not the sort of thing one forgot.
"Your godfather, Sirius Black, had a younger brother. One of Slughorn's prized former students."
Harry paused, the ghost of a name surfacing in his mind. He ventured it carefully: "Regulus Black?"
"More precisely—Regulus Arcturus Black." Sherlock read out the initials distinctly. "R.A.B."
Harry shot to his feet with a startle, eyes wide with shock.
Dumbledore, too, went still. He stared at Sherlock with something close to disbelief.
"He was a Death Eater," Sherlock continued, his tone unchanged. "He came to realize that Voldemort's methods bore no resemblance to the greatness he had imagined, and sought to leave—and was killed by the other Death Eaters for it. Given all of that, he had every reason to track down Voldemort's Horcrux, and every means to do it."
"Exactly—Sherlock's right!" Harry seized on it immediately, his voice charged with conviction. "He was a Death Eater—he would have had access to Voldemort, could have known about the Horcruxes. And if he had a change of heart, of course he'd do everything in his power to bring Voldemort down!"
Compared to Harry's absolute trust in Sherlock, Dumbledore kept cooler counsel.
He shook his head gently, his tone was careful. "Steady, Harry. A name's initials and a history—that may be a stretch. We need more evidence before we draw conclusions."
"No matter," Sherlock said lightly, the hint of a smile at the corner of his mouth. "Conjecture first, verification second. And as it happens, there is someone in this house who can confirm my theory."
"Who?" Dumbledore asked, curious now.
"Me!"
Before Sherlock could answer, Harry leapt up as though he'd been poked with a needle.
"You?" Dumbledore turned to Harry in surprise.
Even Sherlock looked slightly taken aback—because the person he'd had in mind was decidedly not Harry.
"When Sirius first came back here!" Harry's voice shook with excitement, the words tumbling over each other.
"After one of those Order meetings—we were all in the upstairs drawing room doing a clear-out together. While we were going through the old furniture, we found a large golden locket! We passed it round, everyone tried to pry it open—and no one could!"
"And then?" Even Dumbledore, in this moment, could not keep the urgency from his voice.
He had only just been wondering who this mysterious R.A.B. might be.
And now here it was—sought everywhere and found by accident, standing in the lamplight all along.
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