Izzy has spent a decade afraid of elevators for a reason no one else seems to take seriously, not since the night her friends Shayne, Wilma, and Ivan vanished inside an abandoned school and she alone walked out. When she boards a hotel elevator with her father Hayden, joined partway up by Sherry and her teenage daughter Makayla, that old fear stops being irrational the moment the car passes the ground floor and keeps falling to a level that should not exist.

What waits on floor negative twelve is a shifting labyrinth of pipes, hotel corridors, and buildings built to resemble the real world, each one wrong in ways that are hard to name and impossible to ignore. Blueprints signed by a man Izzy believed dead, a stranded SWAT team led by a woman named Gen, and a shape-shifting entity that speaks in the voices of the friends she lost. The realm is still learning how memory works. And Izzy is the one it is learning from.