Three thousand feet of flooded limestone. One way out. And something in the dark that hunts by the beat of your heart.
When a resort developer's drill cracks open a chamber sealed for centuries beneath the jungle of the Yucatan, cave cartographer Mara Cortes is hired to map what lies beyond. What her team finds in the black water of the system they nickname Xibalba is no fossil. It is alive—eyeless, ancient, and patient.
Then the passage collapses behind them.
Trapped in an unmapped labyrinth with their air running out, the survivors learn the terrible rule of the thing that stalks them: it is blind. Light doesn't matter. Hiding doesn't matter. It reads the electric pulse of a living heart—and a frightened heart beats loudest of all. To panic is to die.
As a tropical storm floods the caves and a buried nursery begins to stir, Mara must master her own fear—the same fear that cost her everything once before—or the darkness will listen its way to every last one of them.
