A dense black cloud boiled up in the southeastern sky. It rose high and fast, like a time-lapse movie of the birth of a thunderhead. But it was no rain cloud. Wholly black, it reached up and loomed over her, blocking out the sun. Somehow she knew it was Death coming at her.

Pre-med student Coral is on a vacation in Idaho when something terrible happens. The black cloud is followed by a wildfire and searing heat that lasts for days. She survives deep in a cave but emerges days later to find the world transformed, a world of blackened trees, an ash-filled sky, and no living creatures except her.

So begins her desperate journey: to find water, and food, and other survivors...and the answer to the mystery of what happened.