Harry Potter and the Chamber of Secrets is set in Harry Potter's second year at Hogwarts. In it, there is a mysterious string of petrifications among the school's students. Meanwhile, Harry Potter comes across an enchanted diary, previously owned by one Tom Marvolo Riddle...

In the book's climax, Harry Potter faces Tom Riddle in the Chamber of Secrets, where he learns that Tom Marvolo Riddle is the true identity of Lord Voldemort (the name Lord Voldemort was a pseudonym Riddle invented, as part of an anagram of his full name). Riddle then summons the basilisk, which he had been using attack the students. Harry Potter battles and kills the basilisk, and then destroys the diary (which will, much later in the series, be revealed to have been a horcrux, containing part of Voldemort's fractured soul).