The Diary

"And what may that be, Gilesbie?"; "A – a diary, I believe, sir."; "A diary?"; "Yes…" he replied, "He insisted we don't take that away." (When Sirius Black was sent to Azkaban his belongings included his wand, clothes and a diary he didn't wish to part with. Whose diary was it and why was it so important? Follow Jemima Kingsley's journey through Hogwarts and you may find out)