A Park Service backpacking trip turns deadly when hikers are caught in a steep canyon during a flash flood. Three hikers are swept away, but a rescue team recovers four bodies.

Park Service Investigator Doug Fletcher teams up with rangers Jill Rickowski and Liz Carpenter, and Navajo Nation Policeman Jamie Ballard.

They hike river bottoms and arroyos searching for the origin of the fourth body, leaning on each other to overcome their fears, cultural differences, and emotional baggage. In the process they forge bonds that will last past the end of the investigation.