Mariah Lockwood makes a yearly survey of the patches of ginseng plants, considered an endangered plant. One day she departs into the woods and never returns.

Sheriff Drew Webb calls her daughter, Jessie, who is attending a seminar in Hong Kong, to report her mother missing. Jessie, a PhD involved in ginseng research, returns to her childhood home in Deep Down, Kentucky.

She again meets Drew, from whom she had been separated when a teenager. When Mariah's body is found in one of the ginseng groves, Jessie and Drew find they have several suspects. Ginseng is a valuable commodity in the world market, and someone wants to ensure its availability. Together they try to find the true culprit while fighting their renewed attraction.

Deep Down is a book to read if you want to learn a lot about ginseng. There is more about ginseng plants than the disappearance of Mariah Lockwood. There is little suspense or excitement in the story. There is much discussion about the conflict between Appalachian folk medicine and modern medicine. The author evokes the feeling of time and place with her vivid descriptions of the Appalachian country.