The highest law for House-elf is its master's command. If Regulus wants Kreacher to come home, then it will do everything in its power to get home.
"After Kreacher told Master Regulus everything, he was very worried and told Kreacher to stay in the house and not go out..."
In Voldemort's mind, Kreacher had already been dragged to the bottom of the lake and died long ago by the Inferi.
Regulus's instruction not to let it go out likely stemmed from his suspicion of Voldemort.
"After some time... one evening, young master Regulus came to Kreacher. Kreacher could tell that he was acting strangely, unlike usual."
Kreacher's voice went from choked to sobbing, "He seems to be in a state of mental confusion... He wants Kreacher to take him to the cave, to the cave that Kreacher once went to with the Dark Lord..."
Regulus probably discovered the secret to Voldemort's immortality, namely the Horcrux, an incredibly evil product of Dark Magic.
With a thud, Sirius Black collapsed to the ground, utterly exhausted. "That idiot... why did he have to face it all alone..."
Suddenly, he lunged at Kreacher, shouting, "You went with him, why are you the only one who came back? Why!"
He roared with all his might, raising his fist to smash it down.
The fist, brimming with rage, stopped in front of Kreacher's fleshy nose.
Vincent pulled Sirius Black away from Kreacher, saying, "You're not an impulsive person. Calm down and wait for him to finish."
But Sirius Black, as if possessed, flung Vincent's hand away, shouting, "That cowardly coward must have been unable to stand the filth after drinking that stuff and abandoned Regulus to come back on his own!"
Vincent frowned. "Something's wrong with you right now. House-elf don't disobey their masters. Kreacher would never abandon Regulus."
Sirius Black's bloodshot eyes glared at him fiercely. "How do you know it won't betray you? Maybe the Dark Lord orchestrated all of this!"
Because Regulus discovered the secret of the Horcrux? But that doesn't make sense either. If Voldemort was in cahoots with Kreacher, why did he let him live?
Dumbledore frowned as well.
Sirius Black's behavior was really off; his statements didn't make sense even with the most basic logic, and seemed like a random excuse he made up to vent his emotions.
"Get out of the way, Vincent!"
"Calm down first. Kreacher hasn't explained the whole story yet."
"I said, get out of the way!" Sirius Black suddenly raised his wand and pointed it at Vincent. "This good-for-nothing is a liar, I don't need to listen to him anymore!"
"Alright." Vincent sighed softly, then swiftly grabbed his hand that was gripping the wand.
By the time Sirius Black realized what was happening, he had already been twisted by the arm and pinned to the ground.
Vincent's knee pressed heavily on his lower back, immobilizing him. "Don't blame me, we need to let Kreacher finish what he has to say."
"Let me go!" Sirius Black glared at Vincent with resentment in his eyes. "This is my home, and you all have to listen to me!"
Dumbledore's brow furrowed even deeper.
"Professor, my godfather..." Harry also noticed something was wrong.
Sirius Black may be a bit impulsive and easily angered, but he wouldn't lose his temper to this extent.
Dumbledore pondered for a moment, "I think it must be the house that influenced him, or something in the house."
Harry's hair at the back of his neck stood on end. "Professor, you mean... Horcrux?"
Dumbledore didn't answer him. Instead, he quickly stepped forward, knelt down in front of the immobilized Sirius Black, and pointed the Elder Wand at Sirius's forehead.
The Search Spell quickly located an extremely malevolent aura.
It lurks within Sirius Black's body, constantly manipulating his emotions and judgment.
Dumbledore stared at the small wisp of green mist that had been drawn from the tip of his staff. "Looks like I was right."
Sirius Black's eyes slowly regained their clarity. "What happened to me..."
His face twitched violently. "Whatever happened just now, can you let go of me first? My arm feels like it's about to dislocate."
Vincent looked at his eyes, which had returned to normal, and said, "Of course, I'm just doing this in case."
Sirius Black, now free, quickly shook his arm, which was almost dislocated. "I understand, but could you be a little gentler?"
Vincent spread his hands innocently. "Sorry, I'm used to it. I'll be more careful next time."
Sirius Black was speechless.
It's really unpleasant to be completely controlled like this, unable to resist or move.
Next time? Let's not.
Vincent reached out his hand to him. "How are you feeling now?"
"It's alright." Sirius Black grabbed his hand and stood up, then looked at the small ball of green mist that Dumbledore had imprisoned.
"Was it this thing that made me lose control just now?"
Dumbledore. "It was probably awakened by your strong emotional fluctuations, but I think that's only a small part of it."
Tom's diary came to Vincent's mind.
The soul fragments inside Horcrux can not only manipulate other people's emotions, but also absorb their life force, and eventually even possess a physical form.
If this small wisp of green mist remains inside the body, even if it doesn't completely possess the body, it will absorb the body's vigorous life force.
Sirius Black looked terrified. "Horcrux are truly evil to the extreme."
He looked at Kreacher, who was huddled on the ground trembling. "Did you bring that thing back?"
"Yes...yes." Kreacher suddenly slammed his forehead hard against the carpet, again and again.
"Young Master Regulus wants Kreacher to destroy it, but no matter what Kreacher does, he can't leave a single mark on it... Kreacher is certain that the way to destroy it is to break it from the inside, but he can't open it..."
Kreacher slammed the carpet so hard it became thinner and thinner, and a large bump swelled up on his forehead.
"Stop!" Sirius Black glanced at Vincent behind him. "Kreacher, I order you to stop immediately!"
Kreacher continued to ram the car several more times before finally stopping.
Sirius Black tried his best to remain calm. "You just said Regulus went to the cave with you. What happened between you two afterward, and why was only you the one who came back?"
Kreacher's big eyes were filled with frustration as he slammed his forehead down again.
"Stop! I told you to stop!" Sirius Black shouted at it. "Keep talking! Don't bang your head anymore!"
Kreacher did indeed stop.
It sobbed softly, "Those liquids... those liquids were drunk by young master Regulus..."
"What!?" Sirius Black exclaimed in disbelief. "Why? Why did he drink it himself?"
"Kreacher doesn't... I don't know..." As soon as he finished speaking, tears streamed down Kreacher's face from both sides of his big nose.
"Young Master Regulus gave the fake locket to Kreacher, instructing him to replace Kreacher with the real one when the stone disc became empty..."
Its whimper turned into a sharp cry, "He also ordered... Kreacher to leave, and he also instructed Kreacher ... to go home... and not to tell the mistress... what he had done... and to Kreacher to destroy the locket."
He... Young Master Regulus drank...all the liquid... Kreacher replaced the locket... Young Master Regulus went to the lake...and then...and then he was..."
"Enough!" Sirius Black gasped for breath. "Why didn't you bring him back? Don't you have the ability to do so?"
Kreacher lowered his head, as if he wanted to bang his forehead.
Answer me!
It groaned in agony, "Kreacher tried countless times, but... but Kreacher couldn't take Master Regulus with him... he could only watch helplessly as he was dragged underwater..."
Like the phoenix, House-elf can Apparition with their owners.
However, Kreacher was too old to carry Regulus out of the cave.
"Is that so..." Sirius Black clenched his fist, then let it fall limply. "That fool, if he... if he..."
Unfortunately, reality doesn't offer "what ifs," and no matter how cruel the truth may be, he can only accept it helplessly.