Rebecca Stead, 2010 Newbery Medal winner, signs at Borders

About When You Reach Me: Four mysterious letters change Miranda’s world forever. By sixth grade, Miranda and her best friend, Sal, know how to navigate their New York City neighborhood. They know where it’s safe to go, like the local grocery store, and they know whom to avoid, like the crazy guy on the corner.
But things start to unravel. Sal gets punched by a new kid for what seems like no reason, and he shuts Miranda out of his life. The apartment key that Miranda’s mom keeps hidden for emergencies is stolen. And then Miranda finds a mysterious note scrawled on a tiny slip of paper:
I am coming to save your friend’s life, and my own.
I must ask two favors. First, you must write me a letter.
The notes keep coming, and Miranda slowly realizes that whoever is leaving them knows all about her, including things that have not even happened yet. Each message brings her closer to believing that only she can prevent a tragic death. Until the final note makes her think she’s too late.