The narrator tells us that he was a kid in Japan when his family moved from a small town to a big house in a big city. His parents ran a business, and the narrator's parents were away from home all the time. He used to go home alone, bathe, have lunch, and finish his homework before playing. One day, he heard a strange tapping on the wall. He called for help, but no one was home. He went to his dad's bookshelf and found a book about naval codes. He couldn't figure out the code from the book, so he went back to school.