The sky over Georgia turned the wrong color at 7:42 in the morning, and by noon the Smith family was sealed in a basement with the world they knew gone and something they could not yet name moving through the street above them. What started as a flash on the horizon became a second, then a third, then a fourth — and then a pressure wave that cracked the living room window and put drywall dust in the kitchen air.

Mark Smith spent his entire adult life believing that the things on the news happened to other people in other countries. On Day Zero, he learns the cost of that belief in real time, while his wife — who had quietly prepared for this exact morning — runs a calculation he was never willing to admit she had been running. The highways are already a trap. The broadcasts are cutting out mid-sentence. The man across the street in the bath ...