Uncle Vernon informs the family that he has an important dinner guest coming and that Harry is to stay in his room for the evening.  He has been given Dudley's extra room since they believe that he can do magic now.  Harry is visited by Dobby, a house elf, who warns him not to go back to Hogwarts.  Dobby cannot tell him whose house he works in.  The dinner ruined when Dobby drops food on the guests.  The Dursleys think that Harry did it and lock him in the room and put bars on the windows.

Ron, Fred, and George arrive at Harry's house in a flying car and break Harry out of his room.  They take him to the Burrow, their house.  After the brothers get in trouble from their mother, Harry helps to de-gnome their garden.  Harry and the Weasleys get their book requirements from Hogwarts and they all go to Diagon Alley via Floo Powder.  Harry chokes on the powder when saying the name and arrives in Knockturn Alley by mistake.  He overhears Draco and his father Lucius Malfoy trying to get rid of incriminating evidence from their house.  He is found by Hagrid and led to the book store where he meets Gilderoy Lockhart.  Arthur Weasley and Lucius Malfoy see each other and the scorn that Lucius hold for the Weasley's is evident.

Harry goes with the Weasleys to the train station.  When they try to enter platform 9 3/4, Harry and Ron cannot get through the portal.  They decide to fly in the car to instead.  When they get to the school they start to fall and then they crash into the Whomping Willow.  The car ejects them and their baggage and heads off into the Forbidden Forrest.  Ron and Harry miss the sorting ceremony and are almost expelled.  Ron receives a howler the next day about his taking the car.

Their class learns about mandrakes in Herbology and later Harry is asked by Colin Creevey for an autographed photograph.  They find out that Gilderoy Lockhart is the new Defense Against the Dark Arts teacher and they learn about Cornish Pixies, which the professor is completely unable to control.

Harry starts Quidditch practice where Draco calls Hermione a mudblood.  Ron casts a spell which backfires causing him to spit out slugs for awhile.  Harry has to serve detention with Lockhart when he hears a voice.  He hears it again on the way back from detention.

Harry is invited to Nearly Headless Nick's Deathday Party on Halloween night.  When they leave the party Harry hears the voice again.  He follows the sound and he, Ron and Hermione discover writing on the wall and Mrs Norris, Filch's cat, petrified.  They are questioned about the petrified cat but it is determined that there is no evidence that they did anything wrong.  Hermione asks Professor McGonnogal about the Chamber of Secrets and she tells them that it does not exist.

Hermione gets into the restricted section of the library and finds a book on how to make the Polyjuice Potion, a potion that will allow the drinker to look like another person.  Harry plays in a Quidditch match when a rogue bludger chases him and breaks his arm.  He is still able to catch the snitch and win the game.  Lockhart tries to mend his bones gut instead removes the bones completely.  Madame Pomfrey begins to heal him with Skelgro but he has to stay in the hospital wing.  He starts to hear the voice again when Dobby visits him.  A few minutes later a petrified Colin Creevey is brought in to the hospital.  After Harry get out of the hospital, he finds Ron and Hermione in the girl's restroom where they are preparing the Polyjuice Potion.  Hermione steals the ingredients from Professor Snape's office after Harry creates a diversion in the classroom.

In the DA class, Lockhart and Snape show how to duel.  Harry and Draco duel and Draco creates a snake.  Harry learns he is a Parselmouth when everyone hears him talking to the snake.  It appears to the rest of the class that Harry was urging the snake to attack when he was actually trying just the reverse.  The school in general sees this as an indication that Harry is responsible for petrifying the students.  Harry later look even more suspicious when he happens upon a petrified Justin and a stunned Nearly-Headless Nick.  Harry is taken to see Professor Dumbledore who reveals that he does not suspect him of the crimes.

The Polyjuice Potion is finally ready and Ron and Harry put Crabbe and Goyle to sleep and get some of their hair to add to the potion.  Ron and Harry go to the Slytherin house looking like Crabbe and Goyle and there find out that Draco Malfoy has no idea about who is opening the Chamber of Secrets.  When they get back to the girls restroom they find out that Hermione has used cat fur instead of hair and has turned cat-like.  Hermione goes to the hospital wing.

Harry later sees a flood outside the restroom and notices that Moaning Myrtle's toilet has flooded.  Harry finds a diary belonging to Tom Riddle.  He shows it to Hermione and they begin a search for this person's identity.  Harry later learns the how the diary works.  He writes in it and it answers his questions.  It takes him back in time and he discovers that Hagrid opened the Chamber of Secrets the first time.  After he tells Ron and Hermione about this they decide not to ask Hagrid about it.  A few days pass and Harry, upon returning to his room, finds that his belongings have been trashed and that Tom Riddle's diary is gone.  Harry hears the voice once again after a long absence.  Hermione runs off to the library and later the Quidditch match between Gryffindor and Hufflepuff is cancelled when Hermione is petrified.  Harry and Ron visit Hagrid under the invisibility cloak and they hear Professor Dumbledore, Mr Fudge and Lucius Malfoy (Draco's father) talk with Hagrid.  Hagrid is taken to Azkaban and Professor Dumbledore is suspended as headmaster of the school.  Before Hagrid leaves he gives Ron and Harry a clue for further investigation.

Harry and Ron follow Hagrid's clue about following the spiders and go into the Forbidden Forest.  They meet a giant spider that tells them he is not the monster from the Chamber of Secrets.  He also tells them that he does not harm Hagrid but he cannot save Ron and Harry from his children since that protection does not extend to them.  The flying car reappears and rescues them.  It has apparently gone wild.  It drives them to the edge of the forest and drops them off before returning.

Harry and Ron visit Hermione in hospital and find that she has a piece of paper in her hand.  Apparently she had the answer to the Chamber of Secret and that the monster is a basilisk.  They later find that Ginny has been taken by to the Chamber.  Lockhart, who had been volunteered to help her, attempts to run but Harry and Ron take him with them to Moaning Myrtle's restroom.  Here Harry speaks parselmouth and opens the Chamber of Secrets.  Professor Lockhart tries to escape by using a forget charm with Ron's wand.  The broken wand backfires and causes a cave in.  Harry has to proceed by himself.  Harry finds Ginny unconscious and meets a not fully corporeal Tom Riddle.  He is going to use Ginny's life to give himself substance and live again.  He is the embodiment of Lord Voldemort.  Dumbledore's phoenix, Fawkes, shows up with the sorting hat while Riddle calls up the basilisk.  Harry pulls a sword from the hat while Fawkes pecks out the basilisk's eyes.  Now Harry can look at it without being petrified.  Harry eventually kills the basilisk but gets jabbed by one of its fangs.  He uses the fang to stab the diary and kill the young Voldemort.  Ginny wakes up and Fawkes tears heal Harry from the basilisk's poison.  Harry tells professor Dumbledore and Professor McGonagall about everything and Ginny and Professor Lockhart are sent to the  hospital.  Draco's father Lucius Malfoy and Dobby show up to confront Professor Dumbledore after which Harry tricks Lucius into giving Dobby a sock.  The gift of clothes to a house elf sets it free and Dobby is no longer bound to the Malfoys.