On a sunny September morning, the creatures first appear. Shur sees one of them hovering outside the window in history class: it looks like a giant butterfly, at first too beautiful and strange to seem like a threat. But when emergency alerts light up everyone's phones around her, she realizes something very, very wrong is happening outside. These… things are everywhere.

By the time Shur makes it back to her house with her brother, Keene, and their two best friends, it's clear they must face whatever comes next on their own. A terrifying species the world's never seen before has suddenly emerged, and few living things are safe. As the creatures swarm and attack outside, life for Shur and her friends becomes a survival game. They board the windows, stockpile supplies, and try to make sense of the news reports for as long as the power stays on.

Yet nothing can prepare them for what follows. The butterflies are only the beginning. The next onslaught will be deadlier, and even closer to home.