TL

Every fifty years, Hogwarts holds a secret midnight ball. Only students connected to certain ancient magical families receive invitations. Nobody knows why the ball exists. Y/n receives an invitation despite having no known magical ancestry. At the ball, she meets a mysterious boy wearing a mask. They spend the entire night together without learning each other's names. The next morning, she discovers his mask in her bedroom. And underneath it is a photograph of him. Dated eighty years ago.