The series continues with Harry Potter and the Chamber of Secrets describing Harry's second year at Hogwarts. He and his friends investigate a 50-year-old mystery that appears tied to recent sinister events at the school. Ron's younger sister, Ginny Weasley, enrolls in her first year at Hogwarts, and brings with her a notebook which turns out to be Voldemort's school-time diary. Ginny becomes possessed by Voldemort through the diary and opens the "Chamber of Secrets", unleashing an ancient monster within which begins attacking students at Hogwarts. The novel delves into the history of Hogwarts and a legend revolving around the Chamber. Also, for the first time, Harry realises that racial prejudice exists in the wizarding world, and he learns that Voldemort's reign of terror was often directed at wizards who were descended from Muggles. Harry is also shocked to learn that he can speak Parseltongue, the language of snakes; this rare ability is often equated with the dark arts. The novel ends after Harry saves the life of Ginny Weasley, by destroying a Basilisk and the diary, in which Voldemort saved a piece of his soul (although Harry does not realise this until later in the series). The concept of storing part of one's soul inside of an object in order to prevent death is officially introduced in the sixth novel under the term "horcrux".
The third novel, Harry Potter and the Prisoner of Azkaban, follows Harry in his third year of magical education. It is the only book in the series which does not feature Voldemort. Instead, Harry must deal with the knowledge that he has been targeted by Sirius Black, an escaped murderer believed to have assisted in the deaths of Harry's parents. As Harry struggles with his reaction to the dementors—dark creatures with the power to devour a human soul—which are ostensibly protecting the school, he reaches out to Remus Lupin, a Defence Against the Dark Arts teacher with a dark secret. Lupin teaches Harry defensive measures which are well above the level of magic generally shown by people his age. Harry learns that both Lupin and Black were close friends of his father and that Black was framed by their fourth friend, Peter Pettigrew. In this book, another recurring theme throughout the series is emphasised - in every book there is a new Defence Against the Dark Arts teacher, none of whom lasts more than one school year. In the sixth book, it is implied that the job has actually been jinxed.
