Margaret Peterson Haddix

"Colin has spent all summer solving mysteries with his friend Nevaeh. But they've only ever dealt with other people's mysteries--ones that are safe for Colin to think about. He's still stuck on the mystery surrounding his own father, who his mother refuses to talk about and he can't remember meeting. Then one morning Colin finds a shoebox on his porch with a note on top: 'Your father wanted you to have this.' Inside the box is a key. This new clue...