Harry Potter and the Order of the Phoneix
When Harry is "rescued" from his aunt and uncle, he heads off to the headquarters of the Order of the Phoenix. The Order of the Phoenix is a group assembled long ago when Voldemort was in power long. With Voldemort out and about again, they brought the group together back. At school, things are not much better with Harry's O.W.L.'s (Ordinary Wizarding Level tests) which they are working extremely hard for. As if this is not enough, there is a cruel teacher from the Ministry of Magic who barely teaches them anything useful. Of course, Voldemort...and sadly Sirius...well... you should read the book to find out exactly what does happen.
Books by J.K. Rowling