In May 1889, Frank Brown leads a railroad survey expedition down the treacherous Colorado River through uncharted canyons. Starting from Green River, Utah, with six boats and fourteen men, they navigate the Labyrinth and Stillwater canyons before entering the deadly Cataract Canyon. The expedition faces constant disasters: capsized boats, lost supplies, and violent rapids nicknamed “fountains” that shoot deadly waves without warning. What began as an ambitious engineering survey becomes a desperate fight for survival in the most dangerous waterway in America.