The summer I was twenty, I spent six hours a day in an empty back office reading people’s mail. These people were long dead and their son had sold their papers to the Harvard Theatre Collection, but it still felt partly illicit, and partly like I was solving a mystery--sifting through hundred-year-old clues to find out what had happened. Because something always happened--someone’s always being catty or evasive or finessing the truth (if not…