Plot to steal the Philosopher's Stone

"I knew you would be danger to me straight from the off, especially after Halloween...Snape unfortunately wasn't fooled, when everyone else was running about the dungeon, he went to the third floor to head me off. He, of course, never trusted me again. He rarely left me alone. But he doesn't understand, I'm never alone. Never. Now, what does this mirror do? I see what I desire. I see myself holding the Stone. But how do I get it?"

- Quirinus Quirrell

The plot took place during the Hogwarts 1991–1992 school year, in one of Voldemort's first attempts to gain power. It began with the 1991 Break-In of Gringotts Wizarding Bank and ended with the Battle in the Philosopher's Stone Chambers. After Quirinus Quirrell failed to rob the Stone, his master possessed him at Hogwarts. There they made many attempts to steal the Stone, until June 4, 1992, when Quirrell died.

The stone's origin
The Philosopher's Stone was an extremely powerful magical object. It produced the Elixir of Life and would turn any metal it touched to gold. The only known maker of the Philosopher's Stone was Nicolas Flamel.

Lord Voldemort's situation
In 1981 when Lord Voldemort went to Godric's Hollow seeking out the infant Harry Potter, he met his demise. He remained alive because of his Horcruxes, but existed in a spectral form as his soul had been driven from his body. In this form, he went into hiding in Albania. It was in Albania that he met Quirinus Quirrell, who was abroad gaining first hand experience at Defence Against the Dark Arts. Voldemort, who was still obsessed with gaining power, brought Quirrell over to his way of thinking teaching that there is "no good and evil, there is only power, and those too weak to seek it." Quirrell went into Voldemort's service after this meeting.

The attempted theft at Gringotts
When Nicolas Flamel realised that the Stone may be in danger, he asked his friend Albus Dumbledore for help. The Stone was originally located in Vault 713 in Gringotts Wizarding Bank. Dumbledore arranged to have it moved to a safer location. All the while, Lord Voldemort was determined to rise again. To do this, he would need a corporeal body. He realised that he would regain a physical body if he could drink the Elixir of Life produced by the Philosopher's Stone. Voldemort then planned to steal the Stone in order to make the Elixer. Seeing that a physical body would be needed, Voldemort ordered his follower Quirinus Quirrell to steal the Stone from Gringotts. While Quirrell managed to penetrate the defences of Gringotts, the vault had been emptied, and he failed to retrieve the Stone.

The plot at Hogwarts
Upon arrival at Hogwarts, the Stone was placed in the Third Floor Corridor underneath a trapdoor. The professors of Hogwarts were tasked with aiding in its defence. Once Voldemort learned that the Stone had been removed to Hogwarts School of Witchcraft and Wizardry, he conspired with Quirrell to steal it from the school. As Quirrell had brought Voldemort back into England, Voldemort was on top of the situation and could give Quirrell directions. Quirrell's challenge was to break through all the magical defences the Stone had.

On Halloween he let a troll into the Dungeons of Hogwarts Castle. The was a diversion so he could reconnoiter the defences around the Stone. As Dumbledore was suspicious of Quirrell, he had tasked Severus Snape with keeping an eye on the latter. Fearing that the troll may be a diversion, Snape headed to the third floor corridor to head Quirrell off. During this incident Snape had an unfortunate run in with Fluffy the Three-headed dog that Hagrid had loaned Dumbledore. It was also around this time that Harry Potter became suspicious of Snape thinking that Snape was after whatever Hagrid had retrieved from Vault 713.

Over the Christmas holidays, the Mirror of Erised was placed under the trapdoor as a final layer of protection for the Stone. It was moved to this location after Dumbledore taught Harry how the Mirror worked. Also during this time, Harry, Ronald Weasley, and Hermione Granger began researching Nicolas Flamel. They had heard the name from Hagrid when they had informed him of their suspicions about Professor Snape. It would take them a few more weeks before they discovered his name and learned of the existence of the Philosopher's Stone.

While all this was happening, Quirrell was slowly learning about the defences. He found out about Fluffy on Halloween. Over the proceeding months, he had figured out most of the Stone's defences. After the second Gryffindor Quidditch match, Snape met with Quirrell. He bluntly asked Quirrell about his progress. Quirrell claimed ignorance, but Snape proceeded to threaten him, saying that Quirrell better figure out "where [his] loyalties lie." Harry eavesdropped on this conversation, and it served to convince him that Snape was trying to steal the Stone. Quirrell got one step closer to stealing the stone midway through spring. Hidden under a cloak, he met Hagrid in the Hog's Head. The two drank and played a game of cards; Quirrell purposely lost in order to give Hagrid a dragon's egg. During their conversation, Hagrid let slip the secret of getting past Fluffy.

Later in the term, Harry Potter and Hermione Granger were caught out of bed after hours. They had been helping Hagrid release Norbert, the dragon. Sentenced to detention, they, Neville Longbottom, and Draco Malfoy set out with Argus Filch to serve their detentions. Hagrid took them deep into the Forbidden Forest searching for an injured unicorn. Harry and Malfoy discovered the unicorn, but they also saw a figure drinking its blood. After speaking with Firenze the Centaur, Harry surmised that the figure in the forest was Lord Voldemort. He was drinking the Unicorn blood in order to stay alive. This encounter led Harry, Hermione, and Ron to believe that Snape was trying to steal the Philosopher's Stone for Voldemort.

The attempted theft
It can be assumed that by the end of the term, Quirrell had solved all the defences, because on the final day of exams he sent a fake message to Dumbledore. After Dumbledore had left the school, Quirrell went through the trapdoor. The trio by this time had come to the conclusion that Professor Snape was going to steal the Stone soon. When they asked Professor McGonagall if they could speak with Dumbledore, she informed them that he had left the school. This convinced Harry that the theft was to happen that night. He, Ron, and Hermione went through the trapdoor that evening as well. Quirrell had battled through the obstacles and was waiting in front of the Mirror of Erised when Harry arrived. After Quirrell explained himself to a stunned Harry, he turned his attention back to the Mirror. Voldemort, who had been possessing Quirrell's body, told him to "use the boy." Quirrell then orders Harry in front of the Mirror. Harry looks into it and is given the Stone. When Harry attempted to escape, Lord Voldemort demanded that Quirrell let him speak to Harry directly. Voldemort used Legilimency on Harry and discovered the Stone in Harry's pocket. He ordered Quirrell to seize the Stone. When Quirrell touched Harry, his skin burned and blistered because of the sacrifice Harry's mother made. Harry realized that this was the only way to prevent Quirrell from getting the Stone. He grabbed hold of Quirrell, even though touching Quirrell was also causing him incredible pain. Dumbledore arrived in time to save Harry, but Quirrell died from his injuries when Voldemort left his body.

Aftermath
At Dumbledore's request, the Stone was destroyed. Nicolas Flamel saved enough Elixir of Life to set his affairs in order, and then he died. Harry, Ron, Hermione and Neville were given 170 points overall for Gryffindor and their house won the House Cup. Lord Voldemort's return was further delayed three years.

Appearances

 * Harry Potter and the Philosopher's Stone