Harry Potter and the Prisoner of Azkaban is the third novel in the Harry Potter series, written by J. K. Rowling. The book follows Harry Potter, a young wizard, in his third year at Hogwarts School of Witchcraft and Wizardry. Along with friends Ron Weasley and Hermione Granger, Harry investigates Sirius Black, an escaped prisoner from Azkaban whom they believe is one of Lord Voldemort';s old allies..