At the height of the frontier era, a train races through the Rocky Mountains on a classified mission to a remote army post, carrying passengers who are unaware that they are part of a sinister plot involving murder, conspiracy, and betrayal. As the journey unfolds, a mysterious passenger named John Deakin, an undercover U.S. Secret Service agent, discovers the truth behind the "epidemic" at the outpost and must use his wits to prevent a deadly shipment of arms from falling into the wrong hands.