Harry is finally back at Hogwarts as the Defence Professor. Ron and Hermione have each other and when Neville decides to spend his time with someone else, Harry decides to use his free-time and his access to the Hogwarts library to do something he loves: do research in Defence against the Dark Arts. However, when he reads more about the Patronus charm an interesting information comes to light. What should he do? And why does Snape put up with him all the time? When Luna suddenly needs Harry's help, certain events turn everything up-side down.