Elias is a 12 year boy who is sick with a dreadful disease called consumption. He is moved to an underground place called Mammoth Cave, where there are healing vapors. At Mammoth Cave, Elias is under the care of Doc Croghan. The cave consists of paths, valleys, and rooms, and has blind fish, rivers and seemingly bottomless pits. During his time in the cave, Elias meets Stephen, who is Doc Croghan's slave. He discovers a secret about Stephen.