Charles Bronson, Western action, train adventure and mystery all feature in Tom Gries' mile-a-minute movie about a frontier undercover agent (Bronson) who boards a train to go after a ruthless band of outlaws. On the magnificent old train: bodies are tossed off; cars get detached; there is an epidemic scare; gunrunners and Indians form a cabal to defeat the army; and Bronson and (former boxing champ) Archie Moore engage in a no-holds-barred fight atop the train. The railroad sequences (by second-unit director Yakima Canutt) have been noted as some of the most exciting in screen history. Look for a token appearance by Jill Ireland. Alistair MacLean adapted the screenplay from his own novel.