The second book in the Harry Potter series begins with Harry Potter enduring another miserable summer with his relatives, the Dursleys. As he anxiously awaits his return to Hogwarts School of Witchcraft and Wizardry, a house-elf named Dobby appears in his bedroom. Dobby warns Harry not to return to Hogwarts, claiming that terrible danger awaits him there. When Harry refuses to stay away, Dobby sabotages Harry’s summer, resulting in the Dursleys imprisoning him in his room.
Harry is rescued by his best friend, Ron Weasley, and Ron’s brothers, Fred and George, who arrive in a flying car. They take Harry to the Weasley family home, The Burrow, where Harry experiences warmth and love that contrasts with the neglect he suffers at the Dursleys’. Together, Harry and Ron prepare for their second year at Hogwarts.
Before they can board the Hogwarts Express, the magical barrier to Platform 9¾ mysteriously seals itself. Stranded, Harry and Ron decide to fly the Weasley family’s enchanted car to school. They crash into the Whomping Willow, a violent tree on Hogwarts grounds, damaging the car and getting into trouble with Professor Snape.
As the school year begins, strange and terrifying events unfold. Students are found petrified, starting with Argus Filch’s cat, Mrs. Norris. Messages written in blood appear on the walls, warning that « The Chamber of Secrets has been opened. » According to legend, the Chamber was created by Salazar Slytherin, one of the school’s founders. It is said to contain a monster that only Slytherin’s heir can control, and that it will purge the school of non-pureblood students, known as « Muggle-borns. »
Harry, Ron, and Hermione investigate the mystery. They suspect Draco Malfoy, a pureblood student from Slytherin House, of being the heir of Slytherin. Using Polyjuice Potion, a complex magical brew that allows them to assume other people’s appearances, they disguise themselves as Draco’s friends to interrogate him. They discover that Draco is not the heir but learn little else about the Chamber.
Meanwhile, Harry begins hearing a mysterious voice speaking in Parseltongue (the language of snakes), a rare ability he possesses. This leads the trio to believe the monster in the Chamber is a serpent. Suspicion falls on Harry himself, as speaking Parseltongue is associated with dark wizards.
The trio eventually discovers a clue in an old diary belonging to Tom Riddle, a former Hogwarts student. Through the diary, Harry learns that Tom accused Hagrid, the Keeper of Keys, of opening the Chamber years ago. When Hagrid is sent to Azkaban, Harry and Ron follow his cryptic advice to « follow the spiders. » This leads them to the lair of Aragog, a giant spider, who reveals that Hagrid was innocent and that the true monster resides within the school.
The mystery deepens when Hermione is petrified, leaving behind a torn page from a library book. From this, Harry and Ron learn that the monster is a Basilisk, a giant serpent whose gaze can kill. Its victims are only petrified because they saw the creature indirectly—through reflections or other means. The Basilisk travels through Hogwarts via the school’s plumbing system.
When Ron’s younger sister, Ginny Weasley, disappears, a message reveals that she has been taken into the Chamber of Secrets. Harry and Ron discover the entrance to the Chamber in the girls’ bathroom and descend into its depths with the help of Professor Lockhart, a cowardly fraud who accidentally erases his own memory.
In the Chamber, Harry confronts Tom Riddle, who reveals that he is a memory preserved within the diary. Riddle is actually Lord Voldemort in his younger form, and he has been using the diary to possess Ginny and force her to open the Chamber. Riddle releases the Basilisk to kill Harry, but with the help of Fawkes, Dumbledore’s phoenix, and the Sorting Hat, which provides him with Godric Gryffindor’s sword, Harry kills the Basilisk. He destroys the diary with a Basilisk fang, eradicating Riddle’s memory and saving Ginny.
In the aftermath, Ginny is revived, and the petrified students are cured. Dobby is revealed to be the house-elf of the Malfoy family, and Harry cleverly tricks Lucius Malfoy into freeing Dobby by giving him a sock.
The story concludes with Harry returning to the Dursleys for the summer, knowing he has once again triumphed over Voldemort. The book emphasizes themes of courage, loyalty, and the dangers of prejudice, setting the stage for the challenges Harry will face in the future.