The hospital corridor at eleven at night had a particular kind of quiet that Ivy had learned to hate, the low hum of machines and rubber-soled shoes and nothing else, the sound of a building holding its breath.

Her mother's nurse met her at the nurses' station, face carefully arranged into the kind of calm that meant something had gone wrong and someone had decided Ivy needed to hear it gently.

"What happened," Ivy said, not waiting for the gentle version.

"Your mother's oxygen dropped sharply around eight tonight. We got her stabilized, but her usual medication, the one that's been keeping her heart rhythm steady, wasn't available in the...