"After the Dark Lord left, Kreacher was terribly thirsty and needed water. He crawled to the edge of the island to drink from the Black Lake, but lots of hands came out of the water and tried to pull Kreacher under... Kreacher remembered Master Regulus's orders: go home, go home...
When Master Regulus found that Kreacher had come home, he was very worried. He told Kreacher to hide and not leave the house.
Some time later... Master Regulus came to Kreacher again. Kreacher could tell his mind was in turmoil. Master told Kreacher to take him to the cave, the cave the Dark Lord had visited... Then Master Regulus took a locket out of his pocket, exactly like the Dark Lord's.
He told Kreacher to switch the lockets once the stone basin was empty, then ordered Kreacher to leave and not worry about him... He told Kreacher that he must go home and must not tell Mistress about this, but he must destroy the locket... Then... then he drank all the potion. Kreacher switched the lockets and watched helplessly as Master Regulus was dragged into the water..."
At this point, tears streamed down Kreacher's face. He turned, grabbed the railing, and slammed his head against it.
"Master Regulus forbade Kreacher to tell the family about this. Kreacher told Master Sirius. Kreacher disobeyed Master Regulus's orders... Kreacher did not destroy the locket. Kreacher is not a good house-elf..."
Douglas helplessly restrained Kreacher again, while Sirius stood rooted to the spot, staring blankly at the locket in Douglas's hand. He murmured:
"Is this the locket? The thing Voldemort valued so much. Isn't it just Slytherin's Locket? Why was it worth trading his life for? Tell me why! Surely he didn't think stealing this thing would defeat Voldemort? Stupid idiot..."
Sirius's eyes reddened.