Plot to open the Chamber of Secrets

The plot to open the Chamber of Secrets was an event that first took place in 1943 and later in the 1992–1993 school year. The first plot started with Hogwarts student Tom Riddle locating Salazar Slytherin's legendary Chamber of Secrets and the monster within. It culminated in the death of another student, for which Rubeus Hagrid was framed, and expelled from school. The second plot started with former Hogwarts student Lord Voldemort, once known as Tom Riddle, locating anew the Chamber of Secrets and the monster within. Hagrid again was framed, and sent to Azkaban. The plot culminated in the Petrification of several students and Harry Potter and Ginny Weasley being almost killed. It all ended with Tom Riddle's memory (and a Horcrux) destroyed and the Basilisk killed.

Chamber creation
The Chamber of Secrets was a enormous chamber built by the Founder of Hogwarts and Slytherin House, Salazar Slytherin in the 11th century. The chamber leads from the Second-floor girls' lavatory down through a chute to a circular room. That room has a hole that leads into a large room that has a door at the end of it. One has to speak Parseltongue to open it. The door leads into the main chamber, which is a very large room with a little swimming-pool at the end and a wall-statue of Slytherin himself. The mouth is used to hide an enormous Basilisk, which only emerges when the Heir speaks to it via Parseltongue. On the long way to the end some snake-head statues are to be found. There is also a passage on the right which leads into a walk, with another long walk and a short walk. They both leads to the main chamber. However, in 1992, the circular room had a lot of rat-bones, and the large room with the door at the end was crushed, when Gilderoy Lockhart used Ronald Weasley's wand to perform the Memory Charm which backfired, and caused a lot of rocks to block the way, and the same room had a Basilisk-skin which had been shed.

Tom Marvolo Riddle a.k.a The Heir of Slytherin
In 1926, a half-blood wizard named Tom Marvolo Riddle was born (who would grow up to become the man known as Lord Voldemort), In 1938, Tom Riddle came to Hogwarts and was sorted into Slytherin. He learned about the Chamber of Secrets and Slytherin's heir, and found out, by 1943, that he himself was a direct descendant of Slytherin, and he plotted to purge the school of Muggle-borns, and others unworthy of the gift of magic.

First Stage
In 1943, while Tom Riddle was at Hogwarts School of Witchcraft and Wizardry in Slytherin House and explored the school, he found out he came from the direct line of Salazar Slytherin himself, and he opened the Chamber of Secrets and awakened the Basilisk inside. With this monster he terrorized Hogwarts, petrifying a number of people and killing a Ravenclaw girl named Myrtle, and laid the blame on Gryffindor boy Rubeus Hagrid for it. After what the school thought was the monster was scared away and Hagrid was expelled, the terrifying things ended.

Between Stages
In 1945, Riddle graduated from Hogwarts, and teachers expected him to go on to become an employee at the Ministry of Magic, and in all probability Minister of Magic, but he turned down the offers and worked for Borgin and Burkes. He poisoned Hepzibah Smith to steal his ancestor's locket and Hufflepuff's Cup, when Hepzibah made an opprobrious remark about Burke buying the locket from a ragged woman, Riddle recognised the witch as his own mother. He disappeared from Britain for 10 years and, in 1955, Riddle returned, as Voldemort, to seek the job as Defence Against the Dark Arts professor. Voldemort's first rise to power begins after the job request is turned down and the jinx on the post comes into effect. Voldemort dies in 1981 in an attempt to kill Harry Potter, In 1991-1992, Harry Potter is accepted to Hogwarts School of Witchcraft and Wizardry; Voldemort, who is on the back of Quirinus Quirrell's (the current Defence Against the Dark Arts teacher) head, forced Quirrell to try to steal the Philosopher's Stone and kill Harry Potter, if he could. This failed, and Quirrell died instead, which forced Voldemort to leave the body and search for another way to get back into the wizarding world.

Second Stage
Before the next school year, Death Eater Lucius Malfoy distracted the Weasleys while they were shopping at Flourish and Blotts, and slipped Tom Riddle's Horcrux Diary in the seventh Weasley's cauldron. After the first couple of months, the memory of Tom Riddle took over Ginny, and forced her to petrify several students. Finally, Harry Potter found the diary, but Ginny stole it back from him and then, she finally went down into the Chamber of Secrets, where Tom Riddle's memory came out of the diary and took human form. Harry traveled down to the Chamber and learned Riddle was Voldemort. "So this is what Dumbledore sends his great defender, a songbird and an old hat... Speak to me, Slytherin, greatest of the Hogwarts Four... Let's match the power of Lord Voldemort, Heir of Salazar Slytherin against the famous Harry Potter... Kill him"

- Tom Riddle summoning the basilisk

Riddle then summoned the basilisk, while draining Ginny's life from her. Riddle made it clear that his new goal was to kill Harry Potter instead of the Muggle-born students, since Ginny had revealed to him that Harry was meant to kill him in his future. There was then a battle and the basilisk was killed. Riddle tried to stop a dying Harry Potter from destroying his diary, but failed again. Harry was healed by Fawkes, a phoenix and was saved from death, then, he took the basilisk fang and plunged it into the diary, destroying a Horcrux.

Aftermath
After the battle Harry Potter, with Dobby's tacit hints, was able to correctly surmise Lucius Malfoy's involvement in the opening in the Chamber of Secrets, with Albus Dumbledore concluding that Lucius slipped the diary to Ginny Weasley for personal gain, in hope of sabotaging the Muggle Protection Act her father, Arthur Weasley, had recently proposed in the Ministry of Magic. As the diary lost its magic upon its destruction, there was not sufficient proof for these allegations, though Lucius did lose his position as a Hogwarts school governor for threatening his fellow 11 colleagues, as he had used the incident in an attempt to remove Albus Dumbledore from Hogwarts.

Discovery of Horcruxes
Four years later, In 1997, Albus Dumbledore and Harry discovered Voldemort's Horcruxes. His diary was a horcrux, as were Marvolo Gaunt's Ring, Salazar Slytherin's Locket, Helga Hufflepuff's Cup, Rowena Ravenclaw's Diadem and Nagini. Dumbledore kept to himself the fact that Harry was actually the last Horcrux.

Future openings
In 1998, During the Battle of Hogwarts, Ron Weasley and Hermione Granger opened the Chamber to take a basilisk fang to destroy the Horcrux Cup.

Deaths

 * Moaning Myrtle (1943)

Petrifications

 * Several victims (1942-1943)
 * Mrs. Norris (1992) (Writing on the wall said: THE CHAMBER OF SECRETS HAS BEEN OPENED, ENEMIES OF THE HEIR, BEWARE) (water)
 * Colin Creevey (1992) (camera)
 * Justin Finch-Fletchley (1993) (Saw through Nearly-Headless Nick)
 * Nearly-Headless Nick (1993) (full face, but was already dead, so he was Petrified )
 * Hermione Granger (1993) (mirror)
 * Penelope Clearwater (1993) (mirror)

Appearances

 * Harry Potter and the Chamber of Secrets
 * Harry Potter and the Chamber of Secrets (film)
 * Harry Potter and the Chamber of Secrets (video game)
 * LEGO Harry Potter: Years 1-4
 * Harry Potter and the Half-Blood Prince