Following a string murderers at Isle Royale National Park, park ranger Anna is diagnosed with post-traumatic stress disorder and is forced to take leave. In an effort to lift her spirits, Anne and her husband, Paul, go on a rafting trip in Big Bend National Park. While rafting, though, the two discover the body of a pregnant woman caught between some riverside boulders and branches. Instead of enjoying their vacation in the Chihuahuan Desert, the two commence an investigation into the murder.