What Stalks the Deep - T. Kingfisher

The next installment in the New York Times bestselling Sworn Soldier series,\n featuring Alex Easton investigating the dark, mysterious depths of a coal mine in America.\n Alex Easton does not want to visit America.\n They particularly do not want to visit an abandoned coal mine in West Virginia with a reputation for being haunted.\n But when their old friend Dr. Denton summons them to help find his lost cousin—who went missing in that very mine—well, sometimes a sworn soldier has to do what a sworn soldier has to do...\n