Harry Potter and the Sorcerer's Stone (Book by J. Rowling: Harry never knew who he was, until one day he got a letter telling him that he was a wizard. First book to an awesome series that lets you see how Harry grows into his role as a powerful wizard.
Some days Harry wakes up and has a normal day, except for one thing. His new pet platypus Perry is missing for much of the day. Still, no one tries to kill him on those days and Perry always comes back, so Harry doesn't worry.