She thought about a boy who was given a lesson in place of a parent, and who was careful enough to build exactly what the lesson described, and who had been, until recently, certain he had built the right thing.

She said: "Cassie."

He was very still.

She said: "Before you tell me whatever you're going to tell me, I want you to know that I'm not asking to keep a ledger. I'm asking because I need the whole picture. I need to understand what she had access to and why she used it." She paused. "I need to understand what the thing before me was."

He held her gaze....