In a dystopian future, insurance fraud investigator William Gold arrives in Shanghai to investigate a forgery ring for "papelles", futuristic passports that record people's identities and genetics. Gold falls for Maria Gonzalez, the woman in charge of the forgeries. After a passionate affair, Gold returns home, having named a coworker as the culprit. But when one of Gonzalez's customers is found dead, Gold is sent back to Shanghai to complete the investigation.

Distraught, confused, and half-wild with fear, Sarah Carter emerges alone from the Appalachian cave system where she encountered unspeakable terrors. Unable to plausibly explain to the authorities what happened - or why she's covered in her friends' blood - Sarah is forced back to the subterranean depths to help locate her five missing companions.

After a personal tragedy, Sarah joins her friends on a caving expedition in the Appalachian Mountains. But when a rockfall traps them deep underground, their adventure turns into a nightmare. As they search for a way out, the group discovers they are not alone—lurking in the darkness are savage, cave-dwelling creatures. With rising tension and dwindling trust, the women must fight to survive against both the predators and each other.