As his second year at Hogwarts School of Witchcraft and Wizardry approaches, a young wizard is warned by a house-elf named Dobby about the peril he will encounter if he returns to the magical academy. Dismissing the elf's ominous caution, he reunites with his best friends to solve the mystery of the Chamber of Secrets, a hidden chamber within the school that is said to house a horrific monster. The chamber was purportedly created by one of the school's founders, Salazar Slytherin, and can only be opened by his true heir, with the beast within poised to purge the school of all "Muggle-born" students.

A series of attacks on students, leaving them petrified, spur the trio on their quest. They endeavor to uncover the identity of the heir of Slytherin and delve into the dark history of Hogwarts. Amidst classes, Quidditch, and detentions, they discover that the chamber had been opened once before, and a student died as a result. With the whole school on edge, they must navigate their way through a labyrinth of clues, enchantments, and a betrayal from within their own ranks, racing against time to prevent further calamities as the school edges closer to closure by the governing bodies of the magical world.