In the back corner of Mr. Finch’s history class, by the window overlooking the empty soccer field, Cassandra Cain sits perfectly still. Her desk is a full arm’s length from the one beside it. She watches the door, her dark eyes tracking each entry: the confident stride of the basketball captain, the nervous shuffle of a freshman, the teacher adjusting his glasses by the whiteboard.

The seat next to her is the only one still empty.