Following years of secret atomic testing, a creature within the Wisawa caves – a vast system running from Phantom Lake to the Deadlands – has undergone a horrifying transformation. While exploring the caves, Dr. Vincent Edwards and Rosemary Bennett discover evidence linked to missing children. They report their findings to the sheriff and are asked to lead a rescue mission. Joining them are the sheriff and Stan Johnson, the children's father. The rescue party soon realizes that the caves hold a terrifying unseen danger, one that might be more deadly than the caves themselves.