After the Underwater Investigation Unit’s disbandment, public outcry ushers Sloan McPherson and her partner, former navy diver Scott Hughes, back into the depths of crime solving. But Sloan’s return comes with a personal case. Longtime family friend Fred Stafford has disappeared. Left behind: his abandoned truck in the vicinity of an unmarked sinkhole and new findings that have Sloan second-guessing everything she thought she knew about the man. There are his gambling debts, his association with a treasure-hunting band of underwater cavern junkies called the Dive Rats, and most alarming of all, a discovery in Stafford’s storage shed that raises the stakes even higher and plunges Sloan into an unfathomable mystery. As Sloan’s investigation unfolds, a tragic Florida cold case, local superstitions, and a shocking conspiracy collide. For Sloan, finding Stafford and uncovering the buried secrets of the past soon drag her deeper into the dark unknown than she feared.