The BAU's hunt for a dangerous serial killer leads them deep beneath the city into an abandoned network of tunnels and maintenance corridors. They never make it back out unscathed. When a series of explosions triggers a catastrophic collapse, Y/N is separated from the team and presumed dead. Despite desperate search efforts, no trace of her is found, and the BAU is eventually forced to accept the unthinkable: they've lost one of their own. But Y/N is alive. Trapped in a forgotten section of the underground maze with severe injuries, no way to contact the surface, and a killer who survived the collapse, she finds herself fighting not only for her own survival, but for the lives of several victims still imprisoned below. As the BAU struggles to move forward in the wake of her apparent death, small pieces of evidence begin to suggest the impossible. Y/N may still be alive. Now the team must race against time to uncover the truth, while far below the city, Y/N battles pain, fear, and a relentless killer—determined to survive long enough to find her way home.