Investigator Cassie Dewell is on the trail of a serial killer in the book that inspired the series Big Sky. There's a killer on the road... Helena county has been shaken by the disappearance of two teenage girls. Sisters Danielle and Gracie vanished on a secret cross-country trip to see Danielle's boyfriend, Justin. When rookie cop Cassie Dewell catches her mentor and friend, Investigator Cody Hoyt, planting evidence, he is suspended from the force, his reputation in tatters. He's already drowning his sorrows when his son, Justin, calls. His girlfriend and her sister have disappeared. Unable to investigate himself, Cody turns to his protegee for her help finding the girls. Soon they discover that Danielle and Gracie aren't the first to disappear in the area. When Cody, too, goes missing, it's up to Cassie to find them. Before it's too late.