But then she knows she must go back. The paperback she’s dropped is one of life’s markers, one of experience’s receipts that may be destined to one day disappear; but not on this night, the sixteen-year-old decides, not in this way. Forget sentiment: Her mother’s picture is in the book, which is to say that Molly has left behind identification; and before the doors close — the arc of the imagination bending back to the history it can’t compete with — she steps from the train back onto the landing.