Once, in Beijing, a young girl in a red gown huddled in a doorway. A nice day, bright, the sun moving between tall building willfully. The young girl stared at the sidewalk, waiting for another band of light to finish marching across. Her hands played with the material of her gown, absent-mindedly. She was hungry, but ignored it. Now was not the time.

At last, shade, and the girl stood up, and gently emerged from the doorway. This shadow was fat, and growing fatter, as the sun made its inexorable way. She took a step, and then another. At night,...