The second Harry Potter book begins at the Dursleys – Harry’s Uncle Vernon, Aunt Petunia and Cousin Dudley. Harry, who is “home” for the summer holidays, desperately misses Hogwarts School of Witchcraft and Wizardry. He misses the castle, and Hagrid, and Quidditch. But all his wizard stuff is locked in the cupboard under the stairs. The Dursleys, being non-magical Muggles, hate everything having to do with magic.
Today is Harry’s 12th birthday. Not only have the Dursleys ignored it, they are focused on a dinner party to be given for a business prospect of Uncle Vernon's that night. Harry is expected to sit silently in his room during the party.
Out in the garden, Harry thinks of his friends from Hogwarts - Ron and Hermione - who haven’t written to him all summer. He wants to send Hedwig with a letter, but mustn’t use magic outside Hogwarts.
Just as Harry is remembering his narrow escape from Lord Voldemort last year at Hogwarts, he sees two enormous green eyes in the hedge!! They disappear just as Dudley waddles over to tease Harry about his birthday. Harry scares Dudley by pretending to cast a spell, but is punished by Aunt Petunia with a slew of chores in the hot sun while Dudley lazes about and eats ice cream.
Finally Harry is given a pitiful meal of bread and cheese and sent upstairs just as the doorbell rings. Harry turns to collapse on his bed, only to find someone sitting on it!!!
On the bed is a small, excitable creature with large, bat-like ears, a long thin nose and bulging big green eyes – the eyes Harry’d seen in the hedge. Named Dobby, he explains in a high-pitched voice that he is a house-elf. He is bound to serve one wizard family forever unless the family sets him free.
He’ll have to punish himself for doing it, but Dobby has come to warn Harry that he mustn’t return to Hogwarts. There is a dark plot that would put Harry in mortal danger, but Dobby can’t reveal the details. Uncle Vernon comes up to investigate the noise, and Harry stuffs Dobby in the closet. When the coast is clear, Dobby admits to stopping Harry’s letters so he’ll think no one likes him at Hogwarts. Harry tries to grab the letters, but Dobby jumps away and Harry has to chase him downstairs into the kitchen.
Harry won’t promise to quit Hogwarts, so Dobby tips over Aunt Petunia’s fancy dessert and disappears. Uncle Vernon tries to carry on with the party, but all is ruined when a huge owl swoops into the dining room with a letter for Harry. It’s from the Ministry of Magic, threatening to expel Harry from Hogwarts because he used a Hover Charm. Now Uncle Vernon knows that Harry can’t use magic, so they needn’t be afraid of him. He locks Harry in his room around the clock. After several days, Harry dreams of being caged in a zoo. When he wakes, he looks out the window to see Ron staring in!
Ron and his brothers Fred and George are hovering outside Harry’s window in an enchanted old car. This doesn’t violate the no underage magic rule, since Ron’s Dad is the one who enchanted the car. Fred yanks the bars from Harry’s window using the car, and George picks the lock on Harry’s door so they can get his trunk. They’re about to leave when Harry remembers Hedwig. He leaps back into the room just as Uncle Vernon storms in, and Harry barely manages to escape.
Harry tells them about Dobby. Fred thinks the whole thing is a nasty practical joke, and Harry says it could be his rival Draco Malfoy. George says Draco’s father, Lucius, was a big supporter of ‘You-Know-Who’.
Harry learns that Ron’s Dad’s job at the Ministry of Magic is to take charms off of Muggle-made things – which is ironic since his hobby is to enchant Muggle stuff.
They arrive at Ron’s jumbled old house – the Burrow. They hope to sneak in, but Mrs. Weasley comes out and yells at them. This is Harry’s first visit to a wizard house, and he loves all the cool and bizarre things. Ron’s little sister Ginny is awestruck by Harry.
Mrs. Weasley sends them outside to de-gnome the garden – after consulting a magical guide to household pests, complete with a moving photo of the author. The trick is to swing them in the air and throw them as far as you can over the hedge.
Everyone gets a book list from Hogwarts, and Ron has a letter from Hermione suggesting they meet in Diagon Alley. Ron’s older brother Percy – a Hogwart’s prefect and ace student – joins them for breakfast but acts aloof. The Weasley boys worry if their parents can afford the books and everything for Ginny’s first year at Hogwarts, and Harry thinks privately about all the wizard gold his parents left for him at Gringotts bank.
To get to Diagon Alley, Harry is introduced to floo powder. Sprinkle it on the fire, step in and say where you’re going. Harry chokes on ash, spins very fast, is deafened by a loud roar, and finally falls out into a wizard’s shop devoted to the Dark Arts. Harry starts to leave, but hides when he sees Draco Malfoy coming. Draco’s father Lucius arranges to sell some poisons he’s concerned the Ministry might find if they raid his house. Harry is rescued from a dodgy witch in the alley by Hagrid and then meets up with Hermione and the Weasleys.
They get money from the bank, and the Weasleys need every coin just to buy used stuff. At the bookstore Gilderoy Lockhart, a vain celebrity wizard, is signing his books. He drags Harry up for a press photo, then announces that he will be the new Defense Against the Dark Arts teacher at Hogwarts. Draco taunts Harry, and then Lucius Malfoy taunts Arthur Weasley. The adults get in a fight which Hagrid breaks up.
Summer comes to an end, and Harry and the Weasleys arrive at platform nine and three-quarters for the Hogwarts train. Everyone gets through the barrier except Harry and Ron, who run into solid wall and miss the train.
They take the Weasley’s car and fly toward Hogwarts. After an long flight, just as the castle is coming into view, the car groans, shudders, and then dies. They nosedive toward the castle wall, swerve out over the grounds, and finally crash into a tree – a tree that fights back. The tree pounds them and the car, but at the last moment the engine restarts and they speed backwards out of reach of the tree. The car, which has had quite enough, dumps them and their luggage on the ground and rumbles off angrily.
They boys look through the castle windows as the Sorting starts in the Banquet Hall. Noticing that cruel Professor Snape is not at the staff table, the boys speculate that he might have been fired – just as Snape comes up behind them. He takes them to his dungeon office and informs them that they are in deep trouble because several Muggles saw the flying car. Professors McGonagall and Dumbledore arrive. After a stern lecture, Dumbledore says they aren’t expelled -- this time. After some food they are sent to their dorm. Hermione and Percy are both very upset with them, but everyone else in Gryffindor celebrates their big entrance.
The next morning as Harry is sitting with his friends at breakfast, Ron receives something called a Howler in the mail. Mrs. Weasley's angry voice fills the Great Hall as she yells at him for taking the car. McGonagall comes by with course schedules, and Harry discovers he has Herbology with Prof. Sprout first. During Herbology, Lockhart pulls Harry out and gives Harry a lecture on fame, insinuating that Harry arrived in the car in order to get attention. During Sprout's mandrake lesson, a boy named Justin introduces himself to Harry and his friends. He shares that he's a fan of Lockharts. In the afternoon, Harry meets his own fan, a young boy named Colin Creevey who is enamored with Harry. Draco Malfoy overhears and begins his relentless teasing, but Lockhart enters the scene and comments on Harry's fame again. Later, in Lockhart's class, he gives the students a test on his books. Hermione gets everything correct, even the questions about Lockhart's favorite color and his ideal birthday present. Then Lockhart teaches a lesson on pixies, and Lockhart can't even manage his own lesson. The class ends with Harry and Ron criticizing Lockhart's teaching, and Hermione standing up for him.
Harry is dealing with the stresses of school and looking forward to the weekend. He is awaken by Oliver Wood early on Saturday morning for Quidditch practice. As he heads to the practice, Colin Creavy follows him, and Harry has to explain the rules of Quidditch: there 2 Beaters who have the task of trying to keep the bludgers from knocking people off their brooms. The quaffle is a ball that scores goals, and the fourth ball is the Golden Snitch, which is Harry's job as Seeker, to find it and catch it. If he does so, his team wins the game. As the team practices, Colin snaps pictures, and then the Slytherins show up. Wood asks them to leave, but they have a note from Snape giving them permission. It turns out that Draco is their new seeker. Draco bullies members of the Gryffindor team, and Ron ends up on the bad end of a spell. As Harry and Hermione rush him off to Hagrid, they see Lockhart talking to Hagrid. When the students ask about it, Hagrid insinuates that Lockhart doesn't know what he's doing. Hagrid offers them some refreshments and shows them his garden of pumpkins. When the students return to the school, McGonagall tells Harry that he will be serving his detention with Lockhart. As Harry helps him with his fan mail, he hears a whispering voice talking about killing. Lockhart doesn't hear anything, and the chapter closes with Harry and his friends wondering about what Harry heard.
School continues and by October, everyone is into the routine. Harry is heading in from Quidditch practice when he runs into Nearly Headless Nick, who is upset about not being accepted into the Headless Hunt. Harry is preoccupied with getting better brooms for the team when Filch yells at him for his dirty robes and brings Harry back to his office. As Harry waits for him, he notices a flier for a Correspondence Course in Beginners Magic on Filch's desk and realizes that Filch is not a proper wizard. When Filch realizes Harry has seen it, he lets Harry go on the understanding that Harry won't tell anyone about it. Harry runs into Nick again, and Nick tells him that he will be having a 500th deathday party. On Halloween, Harry, Ron, and Hermione go to Nick's Deathday party in the dungeon. They mingle with the ghosts for awhile, then Harry hears the whispering voice again, saying "time to kill." They run to the hall, and they find Mrs. Norris the cat hanging, dead, near words that read, "The Chamber of Secrets has been opened. Enemies of the heir, Beware." Just then the student body files out of Hogwarts' Halloween feast, and Draco Malfoy arrives, grinning at the sight of the dead cat, and reading the sign aloud, taunting Harry and his friends.
When a very upset Filch arrives, he accuses Harry of murdering Mrs. Norris. Harry and his friends, Filch, and the professors go to Lockhart's office and Dumbledore examines Mrs. Norris, determining that she's been Petrified, which only someone very advanced could do. Filch still accuses Harry, saying that Harry knows he is a "squib" (which Harry later finds out is a person born into a wizarding family who doesn't have magic powers). The students are cross examined by Snape, and Filch wants them to be punished, even though it is revealed that the cat can be revived. Dumbledore lets the students go. During the next few days, Hermione tries to remember what she's heard about the legend of the Chamber of Secrets. In class, she asks Prof. Binns and gets him to tell the story of how, according to legend, Salazar Slytherin (who the house is named for) built a hidden chamber in the school that was sealed until an heir would unseal it and unleash a horror on the school that would cleanse the school of all those unworthy to study magic. The students begin their own detective work, and discover that the message about the chamber is near a women's bathroom that is inhabited by the ghost Moaning Myrtle. They also begin to suspect that Malfoy is the heir of Slytherin, as he comes from a family that believes in pure wizarding blood. The students come up with a plan to get some Polyjuice Potion that will disguise them as other people, so they can find out about Malfoy.
Lockhart makes Harry his teacher's pet, and begins bringing him up to the front of the class to act out stories from his books. Capitalizing on Lockhart's vanity, the students ask him for permission to take out the restricted book in the library on potions, saying they were influenced by his book. When they get the book, they return to Moaning Myrtle's out of order bathroom and flip through the book to find Polyjuice potion, discovering that it will take them a month to prepare and gather all the hard to find ingredients. On Saturday, Harry plays in the the Quidditch match. During the game, it appears that someone has tampered with the bludger, causing it to go after Harry. It hits him and breaks his arm, just before he grabs the Snitch (and winning the game) and falls to the ground. After a bungled attempt by Lockhart to cure Harry, he ends up in the infirmary. That night Dobby shows up and admits the Bludger was his, to persuade Harry to go home. Dobby knows about the Chamber of Secrets but won't (or can't) tell Harry. Dobby leaves when Dumbledore shows up at the infirmary with a Petrified Colin Creevey, who had been on his way to visit Harry in the infirmary. Dumbledore figures that this must mean the Chamber of Secrets has opened again, but there are many more questions than there are answers.
Harry is released from the infirmary and finds Ron and Hermione in Moaning Myrtle's bathroom working on the potion, which is only half finished. Fear is sweeping the school, and people are buying protective amulets and charms. Harry, Ron, and Hermione decide to stay at school over the holidays because Draco Malfoy is staying. But first they need the remaining ingredients, so Harry creates a diversion in Potions class by making Draco's friend Goyle's potion explode while Hermione slipped into the storeroom and took the rest of the needed ingredients. They sign up for a Dueling Club, taught by Lockhart and Snape. Harry and Malfoy are partnered, and in a demonstration in front of the group, Malfoy sets a snake on Harry, which is in danger of attacking Justin Finch-Fletchley. Harry uses his talent for talking to snakes and tells it to stop. Everyone is shocked that he is a Parcelmouth, and they are afraid of him, because Slytherin was a Parcelmouth. Harry overhears a group of students in the library who suspect he is the Dark Wizard. As he storms off to find Justin and explain what really happened with the snake, he runs into a Petrified Justin and Nearly Headless Nick on the stairs. Peeves the Poltergeist, another ghost who lives in the castle, comes across them and yells the alarm. As everyone rushes to the victims, it appears that Harry is caught in the act. McGonagall takes him up a spiral staircase to a special section of the castle where Dumbledore lives.
Harry is left in Dumbledore's office, and sees the Sorting Hat. He puts it on to find out if he was put in the right House, and the hat tells him that he would have done really well in Slytherin. Harry pulls the hat off, upset, and looks over at Dumbledore's sick-looking bird. Just at that moment the bird bursts into flames. Harry calls out, and Dumbledore comes and tells him that the bird Fawkes is a phoenix that will be reborn from the ashes. Hagrid bursts in and comes to Harry's defense, and Dumbledore says he doesn't think Harry did anything, but he wants to talk to him. Alone again, Dumbledore asks Harry if he has anything he wants to share. Harry thinks about the voices, but doesn't tell Dumbledore. Over Christmas, almost everyone leaves except Malfoy and his henchmen Crabbe and Goyle. On Christmas day Hermione tells them that the potion is ready, and after the Christmas feast, they drug Crabbe and Goyle and steal some hair. Hermione has hair from a Slytherin girl Millicient Bulstrode. They change, but Hermione stays in the bathroom and doesn't want to show herself. Harry and Ron (as Crabbe and Goyle) find Malfoy, who shows them an article about Mr. Weasley getting fined for the bewitched car. Malfoy makes fun of Colin, and wishes aloud that he knew who the heir was. He says his father won't tell him about the time 50 years ago when the chamber was opened. When the boys begin to change they run back to the bathroom to find Hermione was accidentally turned into a cat.
Hermione stays in the hospital wing for a week while the potion wears off. Harry and Ron visit her, and on the way out they find Filch upset about water coming from Moaning Myrtle's bathroom. Myrtle, miserable as always, said someone threw a book at her. Harry picks up the book and finds it is a blank diary that belongs to T.M. Riddle, a name Ron recognizes as someone who won an award for service to the school 50 years ago. Hermione, all healed, suspects the diary is in invisible ink, and suspects that Riddle had something to do with the Chamber of Secrets. Lockhart plans a Valentine's Day celebration to boost morale, and Harry gets an embarrassing singing valentine from Ginny Weasley. In doing so he drops his books and his ink bottle, and Malfoy grabs the Riddle diary. Harry grabs it back, and notices the book is clean of the split ink. Alone, Harry tries writing in the diary, and the diary writes back! Tom Riddle tells him that he stopped the person who had opened the chamber. He brings Harry into his memory of Tom requesting to stay at the school over the summer. He is refused, due to the attacks. Riddle hides in the dungeon and catches a large boy named Rubeus who Harry recognizes, with a creature in a cage. He attacks the creature, saying that the attacks must be stopped. Harry is thrown out of the memory and back into his dorm just as Ron enters. Harry quickly tells Ron that the boy Rubeus from the memory was Hagrid: Hagrid had opened the Chamber 50 years ago!
Harry, Ron, and Hermione don't want to believe that Hagrid was responsible for opening the Chamber. Over Easter, the students choose their classes for the next year, and Harry doesn't know what areas he's particularly talented in, so he just signs up for the same classes as Ron. Harry returns to his room one day to find that someone has ransacked his things and stolen Riddle's diary. Before a Quidditch game, Harry hears the whispering voice again and Hermione has an epiphany, and she runs off to the library before she can explain. The Quidditch match is cancelled right before it starts, due to a double attack on Hermione and another girl in the library. They were found petrified next to a small mirror. All extracurriculars are cancelled and students are carefully escorted everywhere by teachers. Harry takes out his Invisibility Cloak and Ron and him visit Hagrid, just as Hagrid gets a visit from Dumbledore, Cornelius Fudge, the Minister of Magic, and Draco's father, Lucius Malfoy, who has a high position in the government. The government wants to remove Hagrid and replace Dumbledore with a government appointed headmaster. Dumbledore agrees to step down, but Hagrid is more reluctant. He tells them that if anyone wants to know anything, they should follow the spiders, but no one listens. As they all leave Hagrid's hut, Ron and Harry have a sinking feeling that more attacks will happen with Dumbledore gone.
With Dumbledore gone, the school is terrified. Harry and Ron try to think of what Hagrid's statement about the spiders might mean, but they can't find any spiders in the castle. Malfoy is the only one in high spirits, since his father is the one who got rid of Dumbledore. In Herbology, some students apologize to Harry for ever suspecting him. They've begun to suspect Draco. Harry notices some spiders heading into the Forbidden Forest. Later that night they put on the invisibility cloak again to sneak out and go into the Forbidden Forest with Hagrid's dog, Fang. They follow the spiders and find Mr. Weasley's car in the woods. As they're looking at it, they are swept off their feet by a giant spider. The spider tells another one, Aragog, that he caught these people in the woods, and Aragog tells him to kill them. Harry yells out that they are friends of Hagrid, who is in trouble. Aragog explains that everyone thought he was from the Chamber, but that was a monster, not him, because he would not kill in the school out of respect for Hagrid. He was hatched in a cupboard in the castle and never even saw the girl that the monster from the chamber murdered, which happened in a bathroom. He will not release Harry and Ron, and the car comes to their rescue. Harry and Ron sneak back into the castle, and think about what this means -- the monster is so terrible that not even other monsters will speak it's name. Harry comes to a realization about the murdered girl: it is Moaning Myrtle!
Unfortunately, with everyone being watched so carefully, the boys cannot get to Moaning Myrtle's bathroom. In class, it is announced that exams are a week away, and that the mandrakes are almost ready to make the potion that will revive the petrified people. Ginny comes to Harry with something important to tell him, but she loses the nerve to tell. Harry and Ron manage to sneak off and try to get to the bathroom, but they are caught, and they tell McGonagall that they are trying to visit Hermione. She gives them permission and they find that the petrified Hermione has a paper in her hand that talks about the Basilisk, the King of Serpents. Hermione has written "pipes" below it, and Harry realizes that the snake was traveling through the pipes, and that his how Harry was hearing the voice. They go to report what they know, but the staff is called together. Ginny Weasley has been taken by the heir into the chamber. Harry and Ron run to Lockhart, who is supposed to fight the monster. Lockhart is packing up to leave, and admits that he didn't do anything that was written in his books. They drag him to Moaning Myrtle, and she tells them that she died after seeing two big yellow eyes. Harry finds the passage and opens it using Parceltongue. They find a snakeskin and Lockhart tries to escape, and in doing so blasts the tunnel, separating Harry and Ron. Harry continues on alone, finding a door with a snake carving. He opens it by speaking Parceltongue, and walks through.
In the Chamber, Harry finds Ginny, still alive, but unresponsive. Tom Riddle steps out of the darkness and Harry asks for his help. Tom, a memory from the diary, has been corresponding with Ginny through his diary. She wrote to him about all of her woes, and how she has a crush on Harry. Tom gained power over Ginny and used her to open the Chamber of Secrets. Tom framed Hagrid, to take the blame, and sat in waiting until someone would find his diary and finish Slytherin's goal. Tom tells Harry that he doesn't care about killing "mudbloods" (people who do not have pure wizarding blood) and that his new target has become Harry. Riddle wants to know how Harry escaped Voldemort, and Harry wants to know why he cares. Riddle tells him "I am Lord Voldemort." Fawkes, the phoenix, flies in and drops the sorting hat. Riddle calls the Basilisk, and the phoenix pokes out the snake's eyes. Harry shoves the sorting hat on his head and finds a sword inside it. Harry fights but is bitten by the poisonous snake right before he kills it. The phoenix cries on his arm and heals Harry. Harry plunges the Basilisk fang into Riddle's diary, and Riddle disappears. Ginny wakes up, and they leave the chamber, finding Ron and a confused Lockhart outside, because Lockhart's memory charm backfired and erased his memory. Fawkes flies them through the pipe back to Myrtle's bathroom, and they run to McGonagall's office and push the door open.
In the office, Harry tells the Weasleys, McGonagall, and Dumbledore (who is back) everything that happened. Harry gives Dumbledore Tom Riddle's diary, and Dumbledore tells them all that Tom Riddle was a brilliant student at Hogwarts who traveled everywhere after he left, and became engrossed in the Dark Arts. Riddle became Voldemort, who very little resembled the boy he once used to be. Ginny is sent to the hospital wing, where the petrified patients are being dosed with mandrake juice and are waking up. Harry and Ron are given "Special Awards for Services to the School" and a feast is to be held to celebrate. The boys explain what happened with Lockhart, and Dumbledore pulls Harry aside. Harry tells him that Riddle had said they were very much alike, and the sorting hat had said Harry would do well in Slytherin. Dumbledore explains that the difference between the two is the choices that they make. He tells Harry that it is choices that people make that show what people truly are made of. Then Lucius Malfoy walks in, with Dobby behind him. Lucius is angry that Dumbledore is back, and Harry realizes that Lucius gave the diary to Ginny in Flourish and Botts. He denies it, and Harry runs after him, shoving the diary into a dirty sock. He shoves the package into Lucius' hand, and Lucius throws the sock off to Dobby, thereby setting Dobby free by giving him a gift. Hogwarts celebrates, and the students head home for the summer.