Chamber of Secrets. Harry's second year at Hogwarts, and something nasty lurks beneath.

Hogwarts' new Defence against the Dark Arts teacher, Gilderoy Lockhart, is a continual source of discomfort for Harry, as Lockheart is unbelievably self centred and seems to believe Harry looks up to him. In fact, most of the male students are of the opinion that Lockhart is a prat. The new teacher, author of almost all this year's coursebooks for his subject, continually corners Harry into photo opportunities and leads to Harry becoming known as an attention grabbing lover of limelight. Harry of course is far more interested in keeping his head down, and not being the favourite topic of school gossip. Added to this is the presence of some kind of dangerous monster in the school, and the dire messages which appear scrawled across walls in blood. The legend of the Chamber of Secrets arises, due to the first of these messages. The legend suggests that Salazar Slytherin, one of the four founders of Hogwarts and sole founder of Slytherin House, argued with the other founders about the acceptance of mixed-blood wizards into the school. Slytherin believed that only students born of wizard parents were worthy to be taught at the school. Because of this argument, the legend states, Slytherin left the school. Not, however, before he'd built a secret place within the walls of Hogwarts, the Chamber of Secrets. According to legend, when the heir of Slytherin returns to Hogwarts, the Chamber will be opened again, and all Mudblood wizards will be purged from the school.

Predictably, Harry becomes the prime suspect in the search for the heir of Slytherin after he uses Parseltongue, or the language of snakes, to command a serpent Draco Malfoy conjures in duelling club. Parseltongues are very rare, and the ability was one of the things Slytherin was famous for. Harry and Ron suspect Malfoy, of course, but when Hermione mixes up a Polyjuice potion so that they can impersonate Crabbe and Goyle, Malfoy's henchmen, they find out that Malfoy knows as little about Slytherin's heir as Harry. When Hermione becomes petrified, turned to stone like several students, Mrs Norris the caretaker's cat and the ghost known as Nearly Headless Nick, Harry and Ron are left to find out what's going on, before someone gets killed. Luckily Hermione had worked it out before she was attacked, and a scrap of paper in her hand tells the boys what they are up against. After finding the entrance to the Chamber of Secrets, Ron and Harry become separated by a rockfall, and Harry is left to go on alone. Eventually, he defeats the monster with the help of Fawkes, Dumbledore's phoenix, and the sword of Godric Gryffindor himself. The heir of Slytherin is in fact Voldemort, who left a copy of himself in a diary during his days at Hogwarts, when he was known only as Tom Marvolo Riddle.