Having to spend the summer at the Dursley's especially on his twelfth birthday, Harry finds himself once again in the misery he has been in for the past eleven years whilst staying with them. Having found a strange creature on his bed, a house-elf named Dobby, the elf warns Harry not to return to school lest he be in grave danger. Harry shrugs the warning off and the house-elf wrecks a dinner with Vernon Dursley's boss in a mad attempt to get Harry expelled from Hogwarts. Infuriated, the Dursley's lock Harry inside of his room until one night the Weasley's drive up next to Harry's window and narrowly rescues him.

After spending the rest of the summer at the Burrow, Harry and the Weasley children head off to Platform 9 ¾. Ginny Weasley, the youngest of them all, has begun her first year there. As everyone walks through the barrier in pairs, Harry and Ron, being the last to leave, are ready to make their entrance when they are thrown back by some unknown force. It appears as if they cannot get through the barrier. Spotting the enchanted Ford Anglia that they had arrived in, Harry and Ron put their trunks in the car, turn it invisible and take off in the air, trailing the Hogwarts Express to guide them

Upon arriving at Hogwarts, Harry and Ron crash into the Whomping Willow, as the engine of the car died on them. After barely escaping the brutal fighting tree, with Ron having his wand snapped in half, the two boys watch as the car retreats to the Forbidden Forest. After slipping inside the castle, while half-way through the sorting ceremony, the boys are caught by Severus Snape. They are taken to his office, given a brutal lecture, and then given detention.

The term is utterly disastrous with Howlers, and outrageous lessons with their Defense Against the Dark Arts professor, Gilderoy Lockhart. During the annual Halloween feast, after leaving Nearly Headless Nick's Deathday Party, Harry, Ron, and Hermione began to head off towards the Great Hall in search of catching the remaining time of the feast. But Harry, hearing a voice, leads them in another direction and they come upon the petrified cat of Argus Filch. On the wall is a sign in warning saying the Chamber of Secrets has been opened. Professor Sprout announces that a Mandrake Potion will cure the state of anyone or anything petrified. Shortly after, Lockhart starts up a dueling club, and Malfoy ends up dueling Harry. After Malfoy sets a snake on Harry, Harry converses with it in Parsletongue, and the snake turns on a terrified Justin Finch Fletchey.

After a violent quidditch match concerning a rogues bludger, Harry finds himself with a broken arm that is later deboned completely by Lockhart. As Harry slept through a painful night of regrowing bones in the hospital wing, he is paid a late night visit from Dobby, These him that Harry should have heeded his warning. After hearing commotion outside, Dobby leaves as yet another petrified person is brought in. The first year Gryffindor, Colin Creevey.

A few days later, after overhearing a blood boiling conversation in the library by fellow students that Harry was the possible heir of Slytherin, Harry wandered among the castle. After hearing the strange voice again, he stumbles across the body of Justin and Nearly Headless Nick, both whom were petrified. During Christmas, Hermione finishes a Polyjuice Potion to find out who's behind these attacks and their first suspect is Malfoy, whom ironically, knew nothing about who was behind the attacks going on in the castle. Afterwards, for a certain period of time, the attacks cease and Ron and Harry are led into Moaning Myrtle's bathroom, who claimed that someone threw a book at her. It was diary, fifty years old, containing the memory of Tom Marvolo Riddle.

Sitting up one night, Harry discovers the secret of the diary and converses with Tom Riddle who takes him back in time to show him the culprit of who was the person caught behind the attacks fifty years ago. Rubeus Hagrid, and that explained why he was expelled from school in his third year. After retuning to the present, Harry shares this information with Ron. They slip quietly out of the castle at night with the Invisibility Cloak to go and talk to him. At his hut, Hagrid is arrested by the Minister, and as he leaves he says loudly that if anyone wants to know something, they should follow the spiders. After doing so, the spiders lead them into the Forbidden Forest, right into a colony of bloodthirsty acromantulas. Ron and Harry talk with Aragog, whom was supposedly the monster that killed a girl fifty years ago. As the boys prepare to leave, Aragog sets the acromantulas on them and the barely escape out alive.

As the final quidditch match rolled around, the game was canceled before it even started. Professor McGonagall brings Harry and on up to the hospital wing and show them that Hermione has been petrified, along with a raven claw girl and there was a mirror in between them. The security on the school becomes even more tighter. Harry and Ron manage to get into the hospital wing again, and visit Hermione, where they notice a spare bit of parchment in her hands explaining about a gigantic snake called a basilik. Quickly, the two of them figure out how everyone was attacked, and that the girl who died fifty years ago was Moaning Myrtle. And then later, they hear that Ginny Weasley has been snatched right into the chamber itself. The school was in danger of being shut down by the next day.

The boys take their information to Lockhart, only to discover him trying to escape and they uncover him for the fraud he really is. They force him down to Myrtle's bathroom at wand point and inquire her on how she died and where she died. Having told them that something that killed her took place near the sink, Harry inspects the sink and find the entrance into the chamber, where he speaks in snake language and unlocks it. They force Lockhart down first and follow after. Once down there, Lockhart's attempts to obliviate Harry and Ron's memories but the curse backfires, setting off a cave in that splits Harry apart from Lockhart and Ron. Harry tells Ron to shift some of the rock while he goes looking for Ginny.

Harry finds Ginny's body and Tom Riddle, who turns out to be the young Lord Voldemort and had been enchanting Ginny through the diary.. A confrontation arises and Fawkes arrive with the Sorting Hat which Harry pulls a sword out of to kill the basilik Tim set on Harry, who was bitten by the beast. Harry destroys the diary and Tom Riddle. Ginny awakens, and they leave out of the Chamber with the others, Fawkes flying them high in the air. As Harry is telling his adventure to Dumbledore, Lucius Malfoy comes in with Dobby. Harry tricks Lucius into giving Dobby a sock and therefore setting the poor enslaved house-elf free. Everything returns to normal and Harry leaves for another miserable summer.