Harold Henthorn calls 911 to report that his wife Toni has been gravely injured after falling off of a cliff on a remote trail. National Park Service Special Agent Beth Shott uncovers suspicious details and inconsistencies in Harold’s story.

As Special Agent Shott investigates the suspicious death of Harold’s wife Toni, anonymous letters and phone calls lead authorities to reopen an investigation into the death of Harold’s first wife 17 years earlier.

As the investigation into the suspicious death of Toni continues, Special Agent Shott learns something startling about Harold’s unusual relationship with his sister-in-law. Shott is joined by FBI agent Jonny Grusing who specializes in serial killers.

A search of the Henthorn home leads investigators to expose one of Harold’s biggest secrets. Shott and Grusing, her FBI partner, are confident that Harold murdered Toni, but they must assemble an airtight case with every scrap of evidence they can find.