Sam and Dean Winchester spend their entire lives on the road, hunting supernatural monsters. Over the years, the brothers experienced dozens of bloody adventures. They had to deal with a variety of creatures: from the yellow-eyed demon who killed their mother, to vampires, ghosts, werewolves, fallen angels and deities. Traveling across America and fighting evil spirits, they gain allies - both among people and among the inhabitants of the other world. But every threat they eliminate opens a new door for the forces of evil... Something strange is happening in the town of Brownsdale, Kentucky: travelers passing through these places disappear without a trace. Locals claim that people are disappearing in huge caves near the city. Visiting them without a guide is dangerous; you may never get out. Sam and Dean don't believe this version, and when two young girls disappear in Brownsdale, they begin to investigate. While the brothers hunt for something sinister lurking in Mammoth Cave, it turns out that someone is guarding a terrible secret and is ready to kill the Winchesters to preserve the secret. The book takes place during the tenth season, between the episodes “Hunting Games” and “Halt and Catch Fire.” ".