Hufflepuff Cup was a magical item created by Helga Hufflepuff, one of the four founders of Hogwarts School of Witchcraft and Wizardry. It was a small golden cup with two finely wrought handles, with a badger, the symbol of Hufflepuff House, engraved on the side. Many believed that the Cup possessed many magical powers, but no one has ever confirmed this to be true.
In 1946, before the Dark Lord declared himself Voldemort, he was working at Borgin and Burkes. During that time, he met with Hepzibah Smith, a descendant of Helga Hufflepuff who kept the cup as a priceless heirloom.
Voldemort got close to her to the point that she began showing Voldemort her antique.
That was when Voldemort saw the Cup and the Slytherin locket. Tom Riddle, at the time, knew he had to get these into his possession.
After successfully killing Hepzibah Smith and framing her death on her elf, Tom Riddle stole both artifacts. Using the murder of Hepzibah, Riddle transformed the Cup into a Horcrux. Many years later, he left it in the care of his trusted Death Eater, Bellatrix Lestrange, without specifying that the cup was a Horcrux. Bellatrix still treated the object with extreme importance, storing it in her family vault at Gringotts Wizarding Bank.
Throughout the future memories that Voldemort got, he found that Harry, Ron, and Hermione, who would transform into Bellatrix using the Polyjuice Potion, would gain access to the vault and thus steal the Cup and later on destroy it to cause harm to Voldemort.
But now, by retrieving the Hufflepuff's Cup early, Voldemort was taking another step in securing his plan and preventing anyone from using his Horcruxes against him.
In total, there were seven Horcruxes that Voldemort created.
Tom Riddle's Diary.
Marvolo Gaunt's Ring.
Salazar Slytherin's Locket.
Helga Hufflepuff's Cup.
Rowena Ravenclaw's Diadem.
Nagini.
Harry Potter.
Among the seven, the diary was destroyed some years back, leaving him with just six. He has already retrieved Marvolo Gaunt's Ring, Salazar Slytherin's Locket, and now Helga Hufflepuff's Cup. With his full control over Nagini and Harry Potter, Voldemort considered these two to also be in his possession, leaving only one left.
Rowena Ravenclaw's Diadem.
The object was located at Hogwarts, more specifically, in the Room of Requirement.
To get his last Horcrux, Voldemort has already begun a plan that was ongoing. Through Draco, a vanishing Cabinet inside Hogwarts was being repaired that connected to another one situated at Borgin and Burkes.
Voldemort expects the repairs to be done in a few months, and once completed, Voldemort plans to personally go and regain his last Horcrux.
"Just a few more months and I will be able to get the rest of my souls," thought Voldemort as he felt the urgency.
The corruption of the soul, an unforeseen event due to creating multiple Horcruxes, was beginning to affect Voldemort more. Sometimes, for a brief second, Voldemort would feel like he no longer had control of his emotions and logic and would make a rash decision.
When he first saw the future memories he got at the graveyard about the whole event that was supposed to happen, and how he was going to lose, his first reaction was how foolish Voldemort in the memories was. But now, having experienced the side effect of splitting his soul, he understood how the Voldemort in those memories had his logic and thinking fully corrupted, rendering him stupid.
This time around, Voldemort was going to make sure not to leave any leaking proof or weakness behind that could be used against him later on.
As such, when he was outside the vault, having regained his Horcrux, he immediately threw an Imperius Curse at the goblin and added a false memory, making him believe that Voldemort and Bellatrix came for some gold and confirmed that the Sword of Gryffindor was still in the vault. In the false memory, the goblin also noticed how Voldemort would at one time lose his balance, where Bellatrix had to support him, and also heard Voldemort talking angrily with Bellatrix about how they needed to find out where Harry Potter had escaped to.
Voldemort was certain that Dumbledore was going to learn about this event one way or another.
So, this was a great chance to feed Dumbledore false information and continue his assumption that Voldemort was still sick from the rebirth ritual. By revealing Voldemort's continued interest in the Sword of Gryffindor, Dumbledore could guess that Voldemort still believed the sword in the vault to be genuine rather than a fake.
Now that Voldemort thought about it, he did not mind getting his hand on the real Sword of Gryffindor. That was a weapon that had the power to destroy the Horcruxes, and if possible, Voldemort would like it to be in his possession instead of his enemies.
But Voldemort knew that this was a very difficult task, as the sword was kept by Dumbledore himself, most certainly in the headmaster's office.
All he could do now was wait as other Death Eaters were going to complete their own task.
----
The 3rd of December 1995. A day the whole of Great Britain's wizarding world was going to remember for years to come. While many were waiting for the return of the boy who lived, Harry Potter was declared missing.
The news of the attack on Azkaban spread rapidly, wizards becoming aware that Death Eaters were now on the open. There was also the report that four Aurors were declared missing, most likely dead. Savage, Proudfoot, John Dawlish, and Kingsley Shacklebolt.
That afternoon, the Minister of Magic, Cornelius Fudge, made a declaration on the case.
"After confirming the escape of 10 high-security prisoners from Azkaban in the early morning of today, we have alerted the Muggle Prime Minister of the danger. Although gravely injured, the Head of Enforcers, Madam Amelia Bones, has given every detail of the fight that happened at the prison. With all these clues, we strongly suspect the breakout was engineered by a man with personal experience in escaping from Azkaban, the notorious mass murderer, Sirius Black, cousin of escapee Bellatrix Lestrange. Sirius Black has been reported as a possible unregistered black dog Animagus. Wizards are requested to take precautions and contact the Ministry in case of any clues."