Doug and Jill Fletcher are dispatched to investigate the origin of a human bone discovered inTheodore Roosevelt National Park. Barely set up in the horse campground, they're confronted with the disappearance of a woman and her teen daughter from a nearby campsite .After determining that the missing women are still in the park, the Fletchers coordinate a search effort across the 110 square milesof the park as thunderstorms threaten to ignite lightning fires and the Little Missouri River swells past its banks making portions of the park inaccessible.