Production has Charles Bronson as a government undercover agent who trips up a gang of gun runners, and a marvellous old steam train as setting for most of the plot.Working from a lean Alistair MacLean script (based on his own novel), director Tom Gries forges a brisk and polished cinematic tale in which the mysteries pile up as old No. 9 steams with troops and medical supplies to an army post gripped by a killer epidemic. Even before embarkation, a couple of officers go missing. Then, along the journey, telegraphic contact is lost, bodies hurtle out of the train into gorges, and the train’s rear section containing the relief troops becomes detached. Seasoned support in stock turns is furnished by Ben Johnson as a crooked marshal, and Ed Lauter as an honest army colonel.