This was a rare moment. Voldemort allowed himself a rare moment of rest as he sat in his room in complete victory.
All the plans he made, all the decisions he took, have all been successful. Each piece fell in place exactly where he wanted.
Harry was now in Azkaban.
The closeness to the Dementors would do the job that Voldemort wanted. His spirit would be broken further and further, eroding his sanity and happiness.
Then there was Amelia Bones, one of the most important members of the Ministry of Magic, who was under the complete control of Voldemort. The Dark Lord could easily manipulate the Ministry by using her, and no one would ever expect her.
At the same time, the seed of resentment has been planted among the wizards.
After knowing how the Muggles have treated Harry, how they insulted Lily Potter, and the way they regarded magic, many began questioning themselves.
They have always protected the Muggles behind the scenes, and yet this was how they treated the Wizards. The blind allegiance they had once held to Albus Dumbledore was slowly crumbling.
After it was proven that Voldemort's return was just a myth, the rumours behind Dumbledore's agenda kept growing.
Even some of the members of the Order of Phoenix, like Molly Weasley, did not want to see Dumbledore due to his not taking any action to prevent the mistreatment of Harry Potter caused by his Muggle family.
And finally, there was Sirius Black, captured and imprisoned, his fate sealed by Voldemort's cunning manipulation when he used Polyjuice to appear as Harry in front of Sirius. After capturing Sirius Black, Voldemort wasted no time in implementing his plan.
Covering his disappearance without any suspicion from the Order.
Through the Imperius Curse, it was easy to force Sirius into writing a letter, fabricating a story about his departure in search of Harry Potter.
But Sirius Black was not Voldemort's primary target; he was merely a pawn in the Dark Lord's grand scheme. Voldemort's true objective lay in acquiring one of the Horcruxes, an object that held a fragment of his soul and granted him immortality.
Using Sirius's connection to the Black family home, Voldemort manipulated him into ordering Kreacher, the loyal house-elf, to retrieve the locket. A Horcrux that was hidden within the house. Kreacher, bound by his master's command, obeyed without question, retrieving the locket and delivering it into Voldemort's waiting hands.
Voldemort then covered his tracks well by implanting a false memory in Kreacher's mind, erasing any recollection of the events that had transpired. With that, Voldemort had secured another piece of his soul.
Now, looking at the table in front of him, Voldemort observed the locket.
It was made of heavy gold with a serpentine 'S' in glittering green stone inlay on the front. It was a piece of jewellery originally owned by Salazar Slytherin, and thus its name.
Slytherin's Locket.
Voldemort got it from Hepzibah Smith when he was still Tom Riddle and was working at Borgin and Burkes. He then turned it into his third Horcrux and hid it in a seaside cave.
The cave was one that Voldemort visited when he was still in the orphanage during his childhood. To make it a stronghold for the locket, Voldemort placed different types of security measures.
The very first one was the obvious one. No one could apparate directly inside the cave or disapparate from within the cave. The second one was that Voldemort applied blood payment to open the doorway to the cave. The blood payment would result in weakening whoever was trying to get inside.
These two measures were to prevent muggles and cowardly wizards.
Once inside, an Inferi-infested lake separated the entrance of the cave from the Horcrux. Any attempt to use a Summoning Charm to get the Horcrux would cause one or more Inferi to leap out of the water to block the spell's effect. If the water was disturbed, the Inferi would emerge and attempt to drag the intruder into the water to drown. To get there, one had to find an invisible boat anchored to the cavern wall, as flight was also restricted. The boat was enchanted so that only a single wizard of age could be transported in it.
The Horcrux itself was in a basin filled with a potion that could not be touched, vanished, transfigured, or charmed in any way possible.
The only way to dispose of it was to drink it.
Once drunk, though, it would cause the drinker to experience unbearable burning pain in their insides, to see "terrible things" and re-experience their worst moments and fears of their past, and to be immensely dehydrated. If the drinker still had some strength left after consuming the potion, any conjured water would vanish on them, forcing them to go drink from the lake; upon disturbing the water, an army of Inferi would rise from the lake and attempt to kill the intruder by dragging them under the water and drowning them.
Later on, to test the security of the cave, Lord Voldemort asked Regulus Black, his then-death eater, to fetch him a house elf, and Regulus offered Kreacher, Regulus Black's own house elf.
At that time, Voldemort took the house elf inside the cave and made it drink the Drink of Despair potion to test the security. Upon seeing the security working on Kreacher, the house elf, unable to continue drinking the potion on his own, Voldemort was satisfied and left, leaving Kreacher to be killed by the Inferi.
Unknown to Voldemort at that time, Regulus had given Kreacher the command "come home when he finished his task".
Obeying his master, Kreacher was able to disapparate from the cave and return to his master. As Voldemort considered house elves as creatures of low stature, he never cared to learn that House Elves could apparate out of locations that Wizards and Witches could not, as house elves had their own brand of magic and were not affected by the anti-disapparate magic set by Voldemort in the cave.
When Regulus learned from Kreacher what exactly Voldemort tried to do to his house elf, Regulus became angry and decided to foil Voldemort's plan.
Regulus later had Kreacher take him back to the Crystal Cave. Regulus drank the potion himself and ordered Kreacher to switch Slytherin's Locket with a fake locket and then go home and destroy the "real" locket, leaving Regulus to die in the cave. For the last few seconds, Kreacher was there; he saw the Inferi's hands pulling Regulus into the water.
Regulus also ordered Kreacher to never tell his family what had happened to him.
Kreacher left as ordered but was unable to destroy the locket, despite his many attempts, as a Horcrux could not be destroyed by normal means.