I am the Messenger by Markus Zusak

Ed lived a pretty ordinary, routine life until the day he unintentionally stopped a bank robbery. Little did he know that single act would change his life forever. Soon Ed receives a mysterious message in the mail, a single playing card, the Ace of Diamonds. On that card are 3 addresses. If Ed chooses to play the game, he will have to determine what is located at the addresses and what he must do at each one. Choosing to play, Ed must make his way through town helping (and possibly hurting) others. Only one question remains: Who is sending these messages and why have they chosen Ed to be the messenger?