Set in America during the Great Depression, Emperor of the North is the story of a violent battle of wills between a sadistic train guard, Shack, (Ernest Borgnine) who has vowed no vagrant will ride his train and survive, and a single-minded drifter, Number 1, (Lee Marvin) who is determined to make a lie of the boast.

Bound together by their mutual loathing, Shack and Number 1 hurtle together across America aboard the steam train, locked in a dangerous game of cat-and-mouse, as each seeks to secure their position in local legend by destroying the other.