I think about that a great deal — about how much of what saved us came down to a rule as simple as we don’t keep secrets that make us feel bad, and to a child young enough to still believe her mother meant it.

I had said that rule to Lily a hundred times, the way parents say things, half on autopilot, never imagining it would be tested against a locked steel box under my own bed.

And when it was tested, it held, because she believed it, because I had made her believe it, and that — not my years of training, not Sarah’s warrant, not any of the machinery that came after — that was the thing that actually broke it open.

I say this not to diminish any of the rest.