16 Psyche

Six kilometers beneath the surface of a nickel-iron asteroid, mining engineer Dax Alderton and rookie geologist Romy Sanderlin are the only survivors of a catastrophic tunnel collapse—sealed inside a metal world with twenty days of air and no way to call for help. Their one chance lies in navigating a labyrinth of ancient void spaces threaded through the asteroid's core, climbing toward a surface that might as well be another planet. But the deeper they push into Psyche's secret heart, the more they realize this dead rock has been keeping something extraordinary hidden for four billion years.