When Hannah Morrison takes an environmental consulting job at a South Dakota gold mine, she doesn't expect to have to confront her darkest, most personal fears. Or to deal with her spoiled haute couture model sister Maddie.In the course of her work, as Hannah discovers secret after secret, she realizes that somebody is poisoning the water in the beautiful Black Hills. Unexplainable clusters of cancer have appeared in the area, too. Somebody is behind all of it and people Hannah cares about are starting to disappear.Driven to solve the problem and find those responsible, Hannah finds herself deep underground, trapped in the darkest of spaces—with a murderer.