Light Yagami is a brilliant but bored high school student in Japan.  One day he discovers a notebook lying on the ground and picks it up.  The instructions on the inside say that any one who's name he writes in the book will die.  Thinking it a weird joke he takes it but doesn’t believe it.  Later he tests it out when he hears of a criminal on TV and writes his name in the book.  When the man dies he has to test it again to confirm that it wasn't just a coincidence.  He writes the name and manner of death of a thug threatening a young girl on the street and this also comes to pass.