Harry Potter runs away from the Durleys, and stumbles upon the castle of the Rook, a strange creature steeped in death and blood magic. He decides to stay. (This isn't actually a pre Hogwarts story.)

Harry Potter has been reincarnated into the body of a snake. A snake in a very familiar zoo, one where he meets a strange child version of himself... a Boy, Girl, or Enby-Who-Lived with a dark lord after them. Of course, knowing what could happen to this child, Harry wants to help - but what can a snake accomplish?