Harry Potter is thirteen years old. After an unbearable holiday with the horrible Dursleys, he finds his faithful friends, Ron and Hermione, to take the train back to Hogwarts College. The world of ordinary people, Muggles, like that of wizards, is in turmoil: according to the latest news, Sirius Black, a dangerous criminal close to Voldemort, has escaped from Azkaban prison. The fearsome prison guards will ensure the security of Hogwarts College, because the escaped prisoner is looking for Harry Potter, responsible for the elimination of his master. It is therefore under good guard that the apprentice wizard makes his third return to school. On the program: divination lessons, the making of a shrivelling potion, the training of hippogriffs... But is Harry really safe from the danger that threatens him?