Rowling uses the second book to deepen the series' social and moral complexity:
Students are found "petrified" (turned to stone), and messages appear on the walls written in blood. Harry Potter Y La Camara Secreta J K Rowlin...
Harry and his friends eventually discover that Tom Riddle—a younger version of Lord Voldemort preserved in a magical diary—is the one behind the attacks. Rowling uses the second book to deepen the