Not only was Kreacher stunned by Severus's words, but Sirius, standing nearby, was also frozen in place.
"Wait, wait, what thing are you talking about getting from whom..."
"How do you know!" Kreacher's shriek interrupted Sirius's question. It looked utterly terrified. "No! Kreacher doesn't know! Kreacher doesn't know what you're talking about!"
The elderly house-elf quickly reacted, frantically denying everything.
But by now, pretending not to understand what Severus was referring to was clearly too late.
"He took you into that seaside cave, didn't he?" Severus just looked at it calmly. "Something of Voldemort's was hidden there. You knew about it from the moment it was hidden there, and you were the one who took Regulus there."
Kreacher's eyes widened even further. It stared at Severus in terror, then suddenly clutched its head.
"You evil wizard! You're reading Kreacher's thoughts! You must be reading Kreacher's thoughts!!"
"I haven't done that, Kreacher. Look at this."
Severus took out the fake Slytherin locket he had obtained from Barty.
"You put this one into the lake back then, and brought the real one back with you."
Kreacher, peeking through its fingers, saw what Severus was holding. Its large eyes could no longer hold back, and bean-sized tears streamed continuously from its sockets.
"No... Master Regulus... Master Regulus gave his life... his life to hide the real one! But... but you took it! You took it!"
"Someone else found it, trying to find Voldemort. But the Voldemort problem is resolved now. He is no longer a threat to the Wizarding World. So we need to find the real locket that Regulus and you took from that cave, to dispose of it properly."
"No! Kreacher won't tell the nasty wizard! Kreacher won't say anything! Especially not to the Dark Lord's servant!"
"You know very well that your Master Regulus ultimately betrayed Voldemort, don't you? He was a true believer in pure-blood ideals, a Slytherin heir who inherited Salazar's will. In the end, he did not agree with Voldemort's ideology, so he chose to stop him."
Severus placed a hand on Kreacher's narrow shoulder.
"I believe you understand the choice he made, and you would certainly support his choice."
Kreacher couldn't help but meet Severus's gaze. A unique kind of magic was influencing the house-elf's emotions.
Severus wasn't trying to control its thoughts or mind, merely using minor Legilimency techniques to soothe its emotional state, allowing it to focus on his words without becoming too agitated to communicate.
Kreacher sobbed for a long time. Only after Severus waited patiently did it speak again.
"The drawing-room... a cabinet in the drawing-room that cannot be opened... Kreacher hid it there..."
Upon hearing this, Severus turned and strode quickly towards the spacious drawing-room of the Black Residence. Sirius was still completely in the dark about their conversation, utterly confused about what they were discussing.
Therefore, after Severus left, he didn't follow. Instead, he stared at Kreacher.
"Tell me! What happened! Everything you know!"
Kreacher was very resistant to Sirius's question.
"No! Kreacher cannot tell Master Sirius! He hates Master Regulus! He won't believe anything Kreacher says!"
"I order you as your master! Kreacher! Tell me!" Sirius commanded fiercely.
As the last heir of the Black Family, Kreacher certainly couldn't defy Sirius's order. It closed its eyes and began a painful narration.
Meanwhile, Severus had already found the unopenable cabinet in the drawing-room.
This cabinet was clearly enchanted with house-elf magic by Kreacher, but it didn't take much effort to undo. Soon, Severus retrieved the last Horcrux besides Harry… the real Slytherin locket.
With this Horcrux in hand, no more Horcruxes remained lost. Nagini, the living Horcrux that appeared later in the original work, was a new Horcrux Voldemort created in the mid-to-late stages, so it clearly couldn't exist yet.
When Severus returned to the entrance hall with the Horcrux, Kreacher had finished telling Sirius the story of how it and Regulus had betrayed Voldemort.
The scene was silent. The dog-like Sirius's face didn't show much expression, but his eyes revealed lingering shock.
Just as Kreacher had said, Sirius held absolute stereotypes about his family members. He had always believed his younger brother was just like his parents… an unyielding, absolute pure-blood supremacist.
And today, if he hadn't heard this from Kreacher, a house-elf absolutely incapable of lying to its master, Sirius would never have been able to believe the truth of the matter.
Even hearing it from Kreacher, doubts arose in his heart.
But alongside the doubt was a complex mix of other emotions.
He didn't know how to describe what he was feeling now, nor what emotion he should even display. He was so lost in thought that it took him a long moment to snap back to reality after Severus stood before him, waiting.
Meeting Severus's deep eyes, Sirius instinctively took two steps back.
"..."
"We need to take this to Dumbledore," Severus said, not mentioning anything about Regulus. He added casually, "After that, before Harry is brought back by Lupin, we have one more thing to take care of. If you're free, you can come with me."
Sirius instinctively resisted and objected.
"Why should I go with you?"
"Because I will tell you everything about the choice your brother made back then."
Severus turned and walked towards the main door of the Black house.
"Is that reason enough?"
Sirius watched Severus's retreating back. He gritted his teeth, and ultimately, hurried to catch up!