My husband, Julian, was away on business, and I had been scheduled for a mandatory back-to-back shift that I could not get out of.

It was my nephew Mason’s twelfth birthday party that evening, Lucas’s cousin, and it had seemed, when I planned it that morning, like the safest possible arrangement: a child at his grandparents’ house, surrounded by family, at a birthday party, while his mother worked.

My in-laws’ home was enormous, the kind of house that announces its owners’ wealth from the street.

Wrought-iron security gates.