After a year of adventures at Hogwarts, Harry, Ron, and Hermione return for their second year. However, strange things start happening at the school, including messages on the wall written in blood and attacks on students by a mysterious creature. Harry begins to hear a strange voice that no one else can hear, which seems to be connected to the attacks.

As they investigate, Harry and his friends discover the existence of the Chamber of Secrets, a hidden room at Hogwarts that was built by the school's founder, Salazar Slytherin. According to legend, the chamber contains a monster that only the heir of Slytherin can control. As the attacks continue, suspicion falls on Harry, who is rumored to be the heir.