Harry Potter and the Prisoner of Azkaban is a fantasy novel by British author J. K. Rowling. The third novel in the Harry Potter series, it follows the young wizard Harry Potter during his third year at Hogwarts School of Witchcraft and Wizardry. With his friends Ron Weasley and Hermione Granger, Harry investigates Sirius Black, an escaped prisoner who no one doubts to be one of Lord Voldemort's allies.