Harry Potter and the Half-Blood Prince
by J.K. Rowling
Filch is the Hogwarts castle caretaker and watchman. He has a cat named Mrs. Norris and the two like to go roaming the corridors, looking for misbehaving students. He knows Hogwarts like the back of his hand, and Harry often finds himself trying not to get caught by Filch. In this time of war, Filch has the task of making sure no dangerous items pass into or out of the castle. Filch was born into a wizard family, but he is unable to practice magic (he's a Squib).